Which of the following elements shows polymorphism?

The coefficient of $x$ in the equation $x^2 + px + q = 0$ was taken as $17$ in place of $13$. Its roots were found to be $-2$ and $-15$. The roots of the original equation are:

What do $C$ and $Si$ possess among the following?

Which of the following reactants can be reduced by $SO_2$?
$I$. $O_3 \to$ product
$II$. $Cr_2O_7^{2-} \xrightarrow{H^{+}} $ product
$III$. $MnO_4^- \xrightarrow{H^{+}} $ product
$IV$. $H_2S \longrightarrow $ product

If $z = \sec(y - ax) + \tan(y + ax)$,then $\frac{\partial^2 z}{\partial x^2} - a^2 \frac{\partial^2 z}{\partial y^2}$ is equal to

Which of the following is a component of baking powder?