Relative formula mass comparison via atomic masses

Steps:

• Identify formulas: A. CaCO₃, B. Li₂SO₄, C. MgCl₂, D. KNO₃.
• Use atomic masses: Ca=40, C=12, O=16, Li=7, S=32, Mg=24, Cl=35.5, K=39, N=14.
• Calculate Mr: A=40+12+(16×3)=100; B=(7×2)+32+(16×4)=110; C=24+(35.5×2)=95; D=39+14+(16×3)=101.
• Compare values: B has the highest at 110.

Why B is correct:

• Li₂SO₄'s Mr=110, the sum of atomic masses in its formula, exceeds others per the definition of relative formula mass.

Why the others are wrong:

• A: CaCO₃'s Mr=100, lower due to fewer heavy atoms.
• C: MgCl₂'s Mr=95, lowest from lighter elements.
• D: KNO₃'s Mr=101, slightly below B despite potassium's mass.

Final answer: B