A rational number is a number that can be expressed as a fraction \( \frac{p}{q} \) where \( p \) and \( q \) are integers and \( q \neq 0 \).
Let's analyze the options:
(a) \( \sqrt{3} \) - This is an irrational number because it cannot be expressed as a fraction of two integers.
(b) \( \sqrt{4} \) - This is equal to 2, which is a rational number since it can be expressed as \( \frac{2}{1} \).
(c) \( \pi \) - This is an irrational number because it cannot be expressed as a fraction of two integers.
(d) \( 2 + \sqrt{5} \) - Since \( \sqrt{5} \) is irrational, \( 2 + \sqrt{5} \) is also irrational.
Among the options given, the only rational number is (b) \( \sqrt{4} \).