1)

M_xO_y+2yHNO_3->xM(NO_3)_{2y//x}+yH_2O

Theo PT: x.n_{M_xO_y}=n_{M(NO_3)_{2y//x}}

->{3,06x}/{xM+16y}={5,22}/{M+{124y}/{x}}

->3,06xM+379,44y=5,22xM+83,52y

->2,16xM=295,92y

->M={137y}/x

->x=y=1;M=137(Ba)

-> Oxit: BaO

2)

n_{Ba(NO_3)_2}={5,22}/{261}=0,02(mol)

Ba(NO_3)_2+Na_2CO_3->BaCO_3+2NaNO_3

Theo PT: n_{BaCO_3}=n_{Ba(NO_3)_2}=0,02(mol)

->m_↓=0,02.197=3,94(g)