Which of the following fluorides has the lowest melting point?

Which of the following groups of elements have chemical properties that are most similar?

$A$ solid compound $X$ on heating gives $CO_2$ gas and a residue. The residue mixed with water forms compound $Y$. On passing excess $CO_2$ gas through $Y$,a clear solution $Z$ is formed. On heating $Z$,compound $X$ is recovered. What is compound $X$?
$\mathop X\limits_{solid}$ $\xrightarrow{\text{heating}} CO_2 + \text{residue}$ $\xrightarrow{H_2O} Y$ $\xrightarrow{\text{excess } CO_2} \mathop Z\limits_{\text{solution}}$ $\xrightarrow{\text{heating}} X$

Which one is known as barytes?

Match the following:

Metal	Uses
$1. \text{Be}$	$c. \text{To prepare windows of X-rays}$
$2. \text{Ca}$	$d. \text{To remove air from vacuumized tubes}$
$3. \text{Mg}$	$a. \text{To prepare Grignard reagent}$

Which of the following is true regarding alkaline earth metals?