The answer is 1. CO. A gram-molecular mass is defined as mass in grams numerically equal to the molecular weight of a substance or the sum of all the atomic masses in its molecular formula. Since CO2 and CO has both carbon and oxygen, the gram-molecular mass does not change. For a compound with carbon and oxygen, the molecular mass comes respectively from 12 (atomic mass of carbon) + (2 × 16) (atomic mass of oxygen), which is 44 g.
The formula for magnesium chlorate is Mg(ClO3)2.
Displaced volume:
final volume - initial volume
1 mL = 1 cm³
38.5 mL - 35.0 mL = 3.5 cm³
hope this helps!
B. When scientific understanding changes.