Answer
The right choices: (a), (b), (d) .
Work Step by Step
a) Mg(s) losses 2 electron (reducing agent), O₂ (g) gains 2 electron (oxidating agent) to yield MgO (s) oxide.
b) Cu(s) losses 2 electron (reducing agent), Pt²⁺ in PtCl₂ (aq) gains two electrons forming Pt (s) metal (oxidating agent).
d) This a redox thermal decomposition of sodium azide salt, where Na⁺ ion gain an electron to form Na(s), while nitrogen in N₃⁻ looses an electron to yield nitrogen gas N₂ (g).
