sizeof() is a unary operator that returns the number of bytes occupied by a variable or data type in memory.

All three methods are valid. Option A initializes with size 5, option B auto-determines size from initialization, and option C declares without initialization.

An empty structure in C has a size of 1 byte. This is to ensure each structure instance has a unique address in memory.

strlen() counts characters excluding the null terminator. "Hello" has 5 characters, so strlen(s) returns 5.

The #define directive replaces MAX with 10 during preprocessing. So x = 10 and output is 10. (Note: semicolon after MAX is not needed but doesn't affect the output)

Both syntaxes are correct. C allows initializing 2D arrays with or without explicit braces for each row.

Integer division truncates the decimal part. 5/2 = 2 (not 2.5) because both operands are integers.

getchar() reads a single character from standard input (stdin) and returns its ASCII value.

The == operator compares values. Since a and b both have value 5, the condition is true and "Equal" is printed.

The stdio.h header file contains declarations for standard input/output functions like printf(). Option A is C++, Option C is C++, and Option D is for memory allocation functions.