Income elasticity from Utility function????

[Goyle]

Q - Consumer's utility f(x) is u(x,y) = x^(1/2) + y. Which of the following is true?

A) Income elasticity of both goods x and y is 1

B) Income elasticity of good x is 0

C) Income elasticity of good y is 0

D) Income elasticity of good x is 1 and of good y is 0

answer is b.....plz explain how???

[Devika]

The given utility function shows quasilinear preferences.
Here, good x is quasilinear. Hence, its income elasticity is 0.