The correct answer is C) ** (Exponentiation). To efficiently calculate the power of 2 for a given exponent, you should use the exponentiation operator (**).

To optimize the performance of loops when processing large data, 'loop unrolling' can be used. Loop unrolling reduces loop overhead and can improve data processing speed.

The fread function in C reads data from a file and stores it in memory, making option b) "Memory" the correct answer.

In C, the strncpy() function is used to copy a specified number of characters from one string to another. Unlike strcpy(), it allows you to specify the maximum number of characters to copy, which helps prevent buffer overflows and enhances program security.

In C, a double pointer is a pointer that points to another pointer. It is used to store the address of a pointer variable.

A union allows multiple variables to share the same memory location, making it useful for scenarios where different types of data need to occupy the same memory space.

In C, an array name is a constant pointer that points to the address of the first element in the array.

The "do-while" loop is used in programming to check the condition after executing the block of code at least once. It guarantees that the loop body is executed at least once, as the condition is evaluated after the first iteration. On the other hand, "for" and "while" loops check the condition before entering the loop, and "if" is used for conditional statements, not loops.

Pointers in C are primarily used for dynamic memory allocation. They allow you to allocate and deallocate memory at runtime, which is essential for efficient memory usage and data structure implementation.

In C, arrays are passed to functions by reference, which means that changes made to the array inside the function affect the original array in the caller.