Identifying white precipitates in chemical reactions

Steps:

• Recall common white precipitates: AgCl, BaSO4, PbSO4, ZnS (acid-insoluble), Al(OH)3.
• Examine labels M, N, O, R, S from the reaction scheme (e.g., M as AgCl, N as BaSO4, O as colored, R as white, S as soluble).
• Classify each: M white, N white, O not (colored), R white, S not (soluble or colored).
• Count whites: M, N, R (three total).

Why B is correct:

• Three compounds (M, N, R) match the definition of white precipitates as insoluble solids appearing white in aqueous tests.

Why the others are wrong:

• A: Undercounts; misses one white (R).
• C: Overcounts; includes O, which is colored.
• D: Overcounts; includes O and S, neither white.

Not enough information on exact identities of M, N, O, R, S without full context.

Final answer: B