`c, n_{HCl}=0,1.0,04=0,004(mol)`

PTHH:

$\rm CaCO_3+2HCl\to CaCl_2+CO_2+H_2O \\ 0,002 \leftarrow 0,004(mol)$

`=>m_{CaCO_3}=0,002.100=0,2(g)`

`d, [H^+]=10^{-1,5}(M)`

`=>n_{H^+}=10^{-1,5}.0,15\approx 0,005(mol)`

PTHH:

`Mg(OH)_2+2H^+ \to Mg^{2+}+2H_2O`

`0,0025\leftarrow 0,005(mol)`

`=>m_{Mg(OH)_2}=0,0025.58=0,145(g)`