Which of the following is a pair of amphoteric hydroxides?

If $a>0$,then $\int_{-\pi}^\pi \frac{\sin ^2 x}{1+a^x} d x$ is equal to

When acetylene is passed through a red-hot iron tube,compound $X$ is formed. Which one of the following reactions will yield $X$ as the major product?

If $\left|\begin{array}{ccc}x & x^2 & 1+x^3 \\ y & y^2 & 1+y^3 \\ z & z^2 & 1+z^3\end{array}\right|=0$ and $x \neq y \neq z$,then $1+x y z$ is equal to

The coefficient of $x^4$ in the expansion of $\frac{(1-3x)^2}{(1-2x)}$ is equal to

If a polygon of $n$ sides has $275$ diagonals,then $n$ is equal to