diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..ae4fe0565 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+//'My house number is 42' 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +12,9 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
+
+// address[0] uses array-style index access. Since address is an object, we need to access the property using its property name.
+// It returns undefined because the object does not have a property called 0.
+// We can use dot notation (.) to access the houseNumber property of the object.
+//The original syntax, address[0], uses index access, which is commonly used with arrays. Since address is an object, we need to access the property using its name. address[0] returns undefined because the object does not have a property called 0. We can use dot notation, address.houseNumber, to access the houseNumber property.
\ No newline at end of file
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..ff1335eee 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -11,6 +11,11 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const key in author) {
+  console.log(author[key]);
 }
+
+// for...of does not work with a plain object because the object is not iterable.
+// It throws: TypeError: author is not iterable.
+// for...in iterates over the object's property keys.
+// We can use each key to access the corresponding property value.
\ No newline at end of file
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..833b96da4 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -10,6 +10,12 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
+
+
+/**[object Object] is shown because ${recipe} converts the
+recipe object to a string using JavaScript's default object string representation.
+We need to access recipe.ingredients directly and 
+iterate over the array using for...of.**/
\ No newline at end of file
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..74ab95353 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,13 @@
-function contains() {}
+function contains() {
 
-module.exports = contains;
+    // Return false if obj is null, undefined, an array, or not a non-null object
+    if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+        return false;
+    }
+
+    // Check if the property exists directly on the object
+    return Object.hasOwn(obj, prop);
+  
+}
+
+module.exports = contains;
\ No newline at end of file
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..917f6184a 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -17,19 +17,33 @@ as the object doesn't contains a key of 'c'
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
 
-// Given an empty object
-// When passed to contains
-// Then it should return false
-test.todo("contains on empty object returns false");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+    // Given an empty object
+    // When passed to contains
+    // Then it should return false
+    test("contains on empty object returns false", () => {
+        expect(contains({}, "a")).toBe(false);
+    });
+
+    // Given an object with properties
+    // When passed to contains with an existing property name
+    // Then it should return true
+    test("returns true when passed an existing property name", () => {
+        const inputObj = { a: 1, b: 2 };
+        expect(contains(inputObj, "a")).toBe(true);
+        expect(contains(inputObj, "b")).toBe(true);      
+    });
+
+    // Given an object with properties
+    // When passed to contains with a non-existent property name
+    // Then it should return false
+    test("returns false when passed a non-existent property name", () => {
+        const inputObj = { a: 1, b: 2 };
+        expect(contains(inputObj, "c")).toBe(false);
+    });
+
+    // Given invalid parameters like an array
+    // When passed to contains
+    // Then it should return false or throw an error
+    test("returns false when passed invalid parameters like arrays or primitives", () => {
+        expect(contains([1, 2, 3], "0")).toBe(false);
+    });
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..4e05ac962 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,9 @@
-function createLookup() {
+function createLookup(countryCurrencyPairs) {
+
+    return Object.fromEntries(countryCurrencyPairs);  
+  
+  
   // implementation here
 }
 
-module.exports = createLookup;
+module.exports = createLookup;
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..48016c6f5 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,3 @@
-const createLookup = require("./lookup.js");
-
-test.todo("creates a country currency code lookup for multiple codes");
 
 /*
 
@@ -33,3 +30,23 @@ It should return:
    'CA': 'CAD'
  }
 */
+const createLookup = require("./lookup.js");
+
+test("creates a country currency code lookup for multiple codes", () => {
+    // Given
+    const input = [
+        ["US", "USD"],
+        ["CA", "CAD"],
+    ];
+
+    const expectedOutput = {
+        US: "USD",
+        CA: "CAD",
+    };
+
+    // When
+    const result = createLookup(input);
+
+    // Then
+    expect(result).toEqual(expectedOutput);
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..447773a8b 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,16 +1,53 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+  
+  if (!queryString || queryString.length === 0) {
     return queryParams;
   }
+
+  // Helper to decode '+' as spaces and percent-encoded characters
+  function decodeParam(str) {
+    return decodeURIComponent(str.replace(/\+/g, " "));
+  }
+
+  // Split by '&' to get raw key-value pairs
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    // Ignore empty pairs caused by trailing or duplicate '&' (e.g. "a=1&&b=2&")
+    if (pair.length === 0) {
+      continue;
+    }
+
+    let rawKey, rawValue;
+    const equalIndex = pair.indexOf("=");
+
+    if (equalIndex === -1) {
+      // Key with no '=' (e.g., "key") -> value is empty string
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      // Split on the FIRST '=' only (handles values containing '=', e.g. "a=b-2")
+      rawKey = pair.slice(0, equalIndex);
+      rawValue = pair.slice(equalIndex + 1);
+    }
+
+    const key = decodeParam(rawKey);
+    const value = decodeParam(rawValue);
+
+    // Stretch Goal: Handle duplicate keys by converting to an array
+    if (Object.prototype.hasOwnProperty.call(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;
\ No newline at end of file
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..256e5c9c3 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -38,6 +38,12 @@ test("should replace '+' by ' '", () => {
 });
 
 // Stretch exercise: Handling query strings that contain identical keys
+test("should handle multiple duplicate keys alongside single keys", () => {
+    expect(parseQueryString("tag=js&tag=node&author=CYF")).toEqual({
+        tag: ["js", "node"],
+        author: "CYF",
+    });
+});
 
 // Delete this test if you are not working on this optional case
 test("should store values of a key in an array when the key has 2 or more values", () => {
@@ -45,4 +51,4 @@ test("should store values of a key in an array when the key has 2 or more values
     key: ["value1", "value2", "value3"],
     foo: "bar",
   });
-});
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..79a615cae 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,16 @@
-function tally() {}
+function tally(items) {
+    if (!Array.isArray(items)) {
+        throw new TypeError("Expected an array as input");
+    }
 
-module.exports = tally;
+    return items.reduce((acc, item) => {
+        if (Object.hasOwn(acc, item)) {
+            acc[item] += 1;
+        } else {
+            acc[item] = 1;
+        }
+        return acc;
+    }, {});
+}
+
+module.exports = tally;
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..a7f5f179f 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,29 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("returns counts for each unique item", () => {
+    expect(tally(["a"])).toEqual({ a: 1 });
+    expect(tally(["a", "b", "c"])).toEqual({ a: 1, b: 1, c: 1 });
+  });
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+    expect(tally([])).toEqual({});
+  });
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("returns counts for each unique item", () => {
+    expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+    expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+  });
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws an error when passed an invalid input like a string", () => {
+    expect(() => tally("string")).toThrow("Expected an array as input");
+  });
\ No newline at end of file
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..a1a6deb9c 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -17,13 +17,29 @@ function invert(obj) {
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
-
+{ key: 1 }
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
-
+{ key: 2 }
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+{ "1": "a", "2": "b" }
 // c) What does Object.entries return? Why is it needed in this program?
-
+Object.entries(obj) returns an array of key-value pairs as two-element arrays.
+Object.entries({ a: 1, b: 2 }) returns [["a", 1], ["b", 2]].
 // d) Explain why the current return value is different from the target output
-
+The line invertedObj.key = value; contains bugs:
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+function invert(obj) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    throw new TypeError("Expected a plain object");
+  }
+
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;
\ No newline at end of file