Write a balanced half-reaction describing the oxidation of solid chromium to aqueous chromium(IV) cations.

Cr(s) ⟶ Cr⁴⁺(aq) + 4e⁻  

Explanation:

1. Write the skeleton half-reaction

Cr(s) ⟶ Cr⁴⁺(aq)

2. Balance charge

Add electrons to the side that needs them.

You have 4+ on the right and 0 on the left. You must add 4e⁻ to the right to balance the charge.

Cr(s) ⟶ Cr⁴⁺(aq) + 4e⁻

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-