Question

If an equation is an identity, then how many solutions does it have?

zero
one
infinite

Answer 1

infinite

Answer 2

Infinite. For example, the equation 3+x = 3 + x is an identity. For what values of x does this equation remain true? Of course, any value of x will work. Thus, it has infinite solutions. Doug does make a good point - if the domain (the x values) have been restricted to a finite number, then the identity will have that same number of answers. But, given your choices of 0, 1, or infinite, you definitely want to go with infinite.