Actually Welcome to the Concept of the Odd and Even Functions.
Basically an Even Function is such that,
If there is a function f(x) is positive, then if we replace x as -x, then also it should give a positive function such as,
f(x) = f(-x)
thus, square of any function is always positive, so the answer is, option 2)
===> g(x) = 2x^2 + 1