Question

1; which number is irrational

Answer 1

(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.