which number is irrational?\na. $sqrt{4}$\nb....

# Explanation: ## Step1: Recall the definition of rational and irrational numbers A rational number can be written as a fraction $\frac{p}{q}$ where $p,q$ are integers and $q\neq0$. An irrational number cannot be written as such a fraction. Also, if $\sqrt{n}$ is a perfect - square (i.e., $n = m^2$ for some integer $m$), then $\sqrt{n}$ is rational. ## Step2: Analyze option A $\sqrt{4}=2$, and $2=\frac{2}{1}$, so it is rational. ## Step3: Analyze option B $\sqrt{35}$: There is no integer $m$ such that $m^2 = 35$. So, $\sqrt{35}$ cannot be written as a fraction of two integers, and it is irrational. ## Step4: Analyze option C $\sqrt{49}=7$, and $7=\frac{7}{1}$, so it is rational. ## Step5: Analyze option D $\sqrt{64}=8$, and $8=\frac{8}{1}$, so it is rational. # Answer: B. $\sqrt{35}$