Question

the table shows the chemical formulas for four substances.

substance	chemical formula
2	$\ce{c_{8}h_{18}}$
3	$\ce{ch_{3}ch_{2}br}$
4	$\ce{c_{4}h_{10}o}$

which substances have the same number of carbon atoms?

• substances 1 and 3
• substances 2, 3, and 4
• substances 2 and 3 only
• substances 1 and 2

Explanation:

Step1: Analyze Substance 1

Substance 1 has formula $C_2H_6O$, so number of C atoms is 2.

Step2: Analyze Substance 2

Substance 2 has formula $C_8H_{18}$, so number of C atoms is 8.

Step3: Analyze Substance 3

Substance 3 has formula $CH_3CH_2Br$ (or $C_2H_5Br$), so number of C atoms is 2.

Step4: Analyze Substance 4

Substance 4 has formula $C_4H_{10}O$, so number of C atoms is 4.

Step5: Compare C atom counts

Substances 1 (C=2) and 3 (C=2) have same C atoms.

Answer:

Substances 1 and 3