Ans c
$\lim_{n \to \infty} (\sqrt{n^2 + n} - n)$
= $\lim_{n \to \infty} n(\sqrt{1 + \frac{1}{n}} - 1)$
= $\lim_{n \to \infty} \frac{(\sqrt{1 + \frac{1}{n}} - 1)}{\frac{1}{n}}$
= $\lim_{n \to \infty} \frac{(-n^{2})}{2\sqrt{1 + \frac{1}{n}}} *(\frac{-1}{n^{2}})$
= 1/2