The empirical formula of a compound is CH2O. Which of the following could be its relative molecular mass: 42, 45, 126, 180?

Given atomic masses:
Relative atomic mass of Hydrogen (H) = 1.0
Relative atomic mass of Carbon (C) = 12.0
Relative atomic mass of Oxygen (O) = 16.0

The empirical formula $\text{CH}_2\text{O}$ contains 1 carbon atom, 2 hydrogen atoms, and 1 oxygen atom.

$$\text{EFM} = (1 \times \text{C}) + (2 \times \text{H}) + (1 \times \text{O})$$ $$\text{EFM} = (1 \times 12.0) + (2 \times 1.0) + (1 \times 16.0)$$ $$\text{EFM} = 12.0 + 2.0 + 16.0$$ $$\text{EFM} = 30.0$$

The relative molecular mass (RMM) of a compound is always a whole number multiple ($n$) of its empirical formula mass:

$$\text{RMM} = n \times \text{EFM}$$

We need to find an option that, when divided by 30.0, gives a whole number.

Let's check the options:

• (a) $42 \div 30.0 = 1.4$ (not a whole number)
• (b) $45 \div 30.0 = 1.5$ (not a whole number)
• (c) $126 \div 30.0 = 4.2$ (not a whole number)
• (d) $180 \div 30.0 = 6$ (a whole number)

Only option (d) is a whole number multiple of the empirical formula mass. This means that for this compound, $n=6$, and its molecular formula would be $(\text{CH}_2\text{O})_6$, which is $\text{C}_6\text{H}_{12}\text{O}_6$.

The correct option is d).
$\boxed{\text{d) } 180}$