What happens when KCl, K₂Cr₂O₇, and concentrated H₂SO₄ reacts?
Have a look at the properties of the compounds involved.

Dichromate ($\ce{Cr(VI), Cr2O7^{2-}}$) is a strong oxidant and is reduced to $\ce{Cr(III)}$ if it finds a suitable partner (which then is oxidized).

Here, a potential partner in a redox reaction is chloride: $\ce{2 Cl- + 2 e^{-} -&gt; Cl2}$.