CaF₂ + H₂SO₄ $$ \to $$ CaSO₄ + 2HF

Here, the oxidation state of every atom remains the same so, it is not a redox reaction.

CrO₅ has butterfly structure having two peroxo bonds.



Peroxo oxygen has –1 oxidation state.

Let oxidation state of Cr be ‘x’

CrO5 : x + 4(–1) + 1 (–2) = 0

$$ \Rightarrow $$ x = +6

So, H₂O₂ acts as reducing agent in all those reactions in which O₂ is evolved.

Both FeCl₂ and SnCl₂ are reducing agents with low oxidation numbers.