14 Which of the following is an irrational number? A sqrt (25) B 10.25 C (2)/(3) D sqrt (18)

The correct answer is D) $\sqrt{18}$.<br /><br />An irrational number is a number that cannot be expressed as a fraction of two integers. In other words, it cannot be written as a simple fraction.<br /><br />Let's analyze each option:<br /><br />A) $\sqrt{25}$: The square root of 25 is 5, which is a rational number because it can be expressed as the fraction $\frac{5}{1}$.<br /><br />B) 10.25: This is a decimal number that can be expressed as the fraction $\frac{1025}{100}$, so it is a rational number.<br /><br />C) $\frac{2}{3}$: This is already in the form of a fraction, so it is a rational number.<br /><br />D) $\sqrt{18}$: The square root of 18 cannot be simplified to a whole number or a simple fraction. It is an irrational number because it cannot be expressed as a fraction of two integers.<br /><br />Therefore, the correct answer is D) $\sqrt{18}$.