Which metal is not silvery white?

In the reaction $M + O_2 \to MO_2$ (superoxide),the metal $M$ is

From which of the following minerals is $Ra$ (Radium) obtained?

When $Mg$ burns in air,it produces

Which of the following $s$-block elements forms a nitride directly by reacting with $N_2$?

Which of the following has the highest tendency to undergo the following reaction?
$M^{+}_{(g)} \xrightarrow{\text{aqueous medium}} M^{+}_{(aq)}$