A rational number is any number that can be expressed as the quotient or fraction of two integers, where the denominator is not zero.
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) \( 2 + \sqrt{} \) - It seems there is a typo here because the expression is not complete. If it's supposed to represent a number like \( 2 + \sqrt{n} \) where \( n \) is positive and not a perfect square, then it would typically be irrational. If \( n \) were a perfect square, that could potentially result in a rational number.
Based on the options:
The rational number is (b) \( \sqrt{4} \).