One third of the square root of which number is 0.001

Which number is irrational? a) 16 b) 18 c) 25 d) 36

Which of the following best describes the graph below? a. it is a function, but it is not one-to-one. b. it is a one-to-one function. c. it is not a function. d. it is a many-to-one function.

Me with this one question, and i'll upvote the brainliest answer