Answer:
The answer to your question is the letter d. S
Explanation:
Data
Change of +4 in the oxidation number
Chemical reaction
K₂Cr₂O₇ + H₂O + S ⇒ KOH + Cr₂O₃ + SO₂
Process
1.- Calculate the oxidation numbers following the rules.
Some rules
H = +1 O = -2 Alkali metals = + 1 Alkali earth metals = +2
K₂⁺¹Cr₂⁺⁶O₇⁻² + H₂⁺¹O⁻² + S⁰ ⇒ K⁺¹O⁻²H⁺¹ + Cr₂⁺³O₃⁻² + S⁺⁴O₂⁻²
Elements that changed their oxidation numbers
Cr₂⁺⁶ ---------------- Cr₂⁺³
S⁰ --------------- S⁺⁴
