What product will be obtained when magnesite $\left({\mathrm{MgCO}}_3\right)$ dissolve in hot dilute ${\mathrm{H}}_2{\mathrm{SO}}_4?$

$\mathrm{Ca}+{\mathrm{H}}_2⟶\left[\mathrm{X}\right]\stackrel{+{\mathrm{H}}_2\mathrm{O}}{⟶}\left[\mathrm{Y}\right]+\left[\mathrm{Z}\right]$ 

The total number of atoms in one molecule or formula unit of $\left[\mathrm{Y}\right] \& \left[\mathrm{Z}\right]$ is _____.

Identify the product of the given reaction:

$\mathrm{AgBr}+2{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3⟶$

 ${\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{diluted}\right)+{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3⟶$

${\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{concentrated}\right)+{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3⟶$