Which of the following is not true about potash alum?

Which of the following electronic configurations belongs to $s-$block elements?

Which of the following statements is correct?

Match the following compounds (Column-$I$) with their uses (Column-$II$):

Column-$I$	Column-$II$
$I. Ca(OH)_2$	$A$. Casts of statues
$II. NaCl$	$B$. White wash
$III. CaSO_4 \cdot \frac{1}{2}H_2O$	$C$. Antacid
$IV. CaCO_3$	$D$. Washing soda preparation

$A$ metal $M$ and its compound can give the following observable changes in a sequence of reactions: $M$ $\xrightarrow{\text{dilute } HNO_3} \text{Colourless solution}$ $\xrightarrow{\text{aqueous } NaOH} \text{White precipitate}$ $\xrightarrow{\text{excess } NaOH_{(aq)}} \text{Colourless solution}$ $\xrightarrow{H_2S} \text{White precipitate}$. Identify the metal $M$.

Green vitriol is . . . .