4. The data structure required to check whether an expression contains a balanced parenthesis is?a) Queueb) Stackc) Treed) Array

The data structure required to check whether an expression contains a balanced parenthesis is a Stack (b).

Here's why:

Step 1: Start scanning the expression from the left to the right. Step 2: If the current character is an opening bracket (i.e., '(' or '{' or '['), then push it to the stack. Step 3: If the current character is a closing bracket (i.e., ')' or '}' or ']'), then pop an element from the stack. If the popped bracket is not the matching opening bracket, then the parenthesis is not balanced. Step 4: If you encounter a closing bracket without a corresponding opening bracket in the stack, then also the parenthesis is not balanced. Step 5: Continue this process until all the characters in the expression are scanned. If the stack is empty at the end, then the parenthesis is balanced. If not, then the parenthesis is not balanced.

This process can be easily implemented using a stack, hence the answer is (b) Stack.