C

- Hướng dẫn giải

Chọn C

$\underset{x\to +\infty }{\lim }x\left(\sqrt{x^2+2}-x\right)=\underset{x\to +\infty }{\lim }x\frac{x^2+2-x^2}{\sqrt{x^2+2}+x}=\underset{x\to +\infty }{\lim }\frac{2x}{\sqrt{x^2+2}+x}=\underset{x\to +\infty }{\lim }\frac{2}{\sqrt{1+\frac{2}{x^2}}+1}=1$