24.3 is a rational number since it can be expressed in the form of a fraction: 24.3 = 243/10
7 is a natural number
sqrt(25) = 5, which also belongs to the set of the naturals
sqrt(2) is irrational since there aren't any pair of integers a and b such that sqrt(2) can be expressed in the form a/b
Answer: option B: sqrt(2)