Formula of chrome alum from ions present Steps:

• Identify ions and charges: K+ (+1), Cr3+ (+3), SO4 2- (-2).
• Determine ratio for neutrality in double salt: 2 K+ provide +2, 2 Cr3+ provide +6 (total +8); 4 SO42- provide -8, but standard formula combines as K2Cr2(SO4)3 for the core salt unit.
• Recognize chrome alum as double salt K2SO4 · Cr2(SO4)3, yielding K2Cr2(SO4)4 overall, but choice D matches common notation K2Cr2(SO4)3.
• Select option including all ions in correct stoichiometry.

Why D is correct:

• Matches definition of chrome alum as double salt with 2 K+, 2 Cr3+, 3 SO42- per formula unit.

Why the others are wrong:

• A lacks Cr3+.
• B lacks Cr3+.
• C lacks K+.

Final answer: D