a)
[tex]m_S=32 \ u\\\\m_O=16 \ u\\\\m_{SO_3}=32 \ u+3\cdot16 \ u=32 \ u+48 \ u=\boxed{80 \ u}[/tex]
b)
[tex]m_H=1 \ u\\\\m_{Cl}=35 \ u\\\\m_{HCl}=1 \ u+35 \ u=\boxed{36 \ u}[/tex]
c)
[tex]m_N=14 \ u\\\\m_H=1 \ u\\\\m_{NH_3}=14 \ u+3\cdot1 \ u=14 \ u+3 \ u=\boxed{17 \ u}[/tex]
d)
[tex]m_H=1 \ u\\\\m_P=31 \ u\\\\m_O=16 \ u\\\\m_{H_3PO_4}=3\cdot1 \ u+31 \ u+4\cdot16 \ u=3 \ u+31 \ u+64 \ u=\boxed{98 \ u}[/tex]
