a)
$m_{Ba} = 0,8.137 = 109,6(gam)$
$m_C = 0,8.12 = 9,6(gam)$
$m_O = 0,8.3.16 = 38,4(gam)$
b)
$n_{NH_3} = \dfrac{8,96}{22,4} = 0,4(mol)$
$m_N = 0,4.14 = 5,6(gam)$
$m_H = 0,4.3.1 = 1,2(gam)$
c)
$n_{K_3PO_4} = \dfrac{4,5.10^{23}}{6.10^{23}} = 0,75(mol)$
$m_K = 0,75.3.39 = 87,75(gam)$
$m_P = 0,75.31 = 23,25(gam)$
$m_O = 0,75.4.16 = 48(gam)$