Step-by-step explanation:
(a)
![Na_2S+HCl\rightarrow H_2S+2NaCl](https://img.qammunity.org/2020/formulas/chemistry/college/hwngfnythhwrimziqttnjgru4nt6ix2z51.png)
This is acid base reaction because there is no change of oxidation state on either side of the reaction.
(b)
![2Na+2HCl\rightarrow H_2+2NaCl](https://img.qammunity.org/2020/formulas/chemistry/high-school/f87t5cjyeikqlpxd6vwspfiox9vc6ovw3j.png)
This is a oxidation reduction reaction because sodium in elemental state ( 0 oxidation state) oxidizes to Na⁺ in NaCl. Also H⁺ in HCl reduces to H° in H₂.
(c)
![Mg+Cl_2\rightarrow MgCl_2](https://img.qammunity.org/2020/formulas/chemistry/college/i5sheggoim3phjoxd26vsgu5cnriru324f.png)
This is a oxidation reduction reaction because magnesium in elemental state ( 0 oxidation state) oxidizes to Mg²⁺ in MgCl₂. Also Cl° in Cl₂ reduces to Cl⁻ in MgCl₂.
(d)
![MgO+2HCl\rightarrow H_2O+MgCl_2](https://img.qammunity.org/2020/formulas/chemistry/college/z7xmr53pk7ua7obmumh2rc2a9s0orxg1ky.png)
This is acid base reaction because there is no change of oxidation state on either side of the reaction.
(e)
![K_3P+2O_2\rightarrow K_3PO_4](https://img.qammunity.org/2020/formulas/chemistry/college/hcwkk2fakz226cncntwlj3uhtgwxsux1xr.png)
This is a oxidation reduction reaction because phosphorous in P³⁻ in K₃P oxidizes to P⁵⁺ in K₃PO₄ and oxygen reduces.
(f)
![3KOH+H_3PO_4\rightarrow K_3PO_4 + 3H_2O](https://img.qammunity.org/2020/formulas/chemistry/college/yoozyfxumzwdmwugtg595a7l1nio5azigg.png)
This is acid base reaction because there is no change of oxidation state on either side of the reaction.