If an equation is an identity, then how many solutions does it have?
a. zero
b. one
c. infinite

Option (C) Infinite

Explanation:
In simple words, indentity equation is an equation in which the left hand side of an equation is always equal to the right hand side, regardless of what you insert into it. For example:

15 + x = 15 + x (an identity matrix)

If you put x = 1, the equation would become 16 = 16 (LHS = RHS);
If you put x = 2, the equation would become 17 = 17 (LHS = RHS); and so on...

As you can see whatever value of x you put into the equation, the equation is always an identity matrix.

Hence the solutions to the equations will Infinite (which is option C)