When acidified K_2 Cr_2 O_7 solution is added to Sn^(2+) salts, then Sn^(2+) changes to:

Explanation :

As K₂ Cr₂ O₇is an oxidizing agent it will oxidize the Sn²⁺ Oxidation means loss of electrons.

So Sn²⁺  will oxidize to its highest oxidation state and changes to Sn⁴⁺