1; which number is irrational √4 1/3 0. √6 -25 natural whole integer rational irrational which set of numbers does √13 belong irrational number whole numbers natural numbers intergers

(1) which number is irrational?   
√4
1/3
0.14...
√6
Focus first on the definition of "rational."  A "rational number" is formed by taking the ratio of two integers.  

sqrt(4) = 2/1 (or just 2) is rational.

1/3 is the ratio of two integers and thus is rational.

0.14 is the ratio of 14 and 100 (whole numbers), and thus is rational.

sqrt(6) cannot be written as the ratio of integers, and thus is irrational.