Which group of elements has approximate atomic weights of 10, 12, 14, 16, and 18?

• A. B C N O F
• B. Cl Na H Ca
• C. H He Li Be
• D. C N O S

Answer: (A)

The main idea here is matching a set of light elements by their approximate atomic weights. The group that includes boron, carbon, nitrogen, oxygen, and fluorine has atomic weights about 11, 12, 14, 16, and 19. If you round those values to the nearest whole number, you get roughly 10, 12, 14, 16, and 18, which fits the given numbers. This sequence comes from elements in the same region of the periodic table, showing a steady increase in weight as you move from boron to fluorine.

The other groups don’t line up with those rounded weights. For instance, a mixed group like chlorine, sodium, hydrogen, and calcium spans a wide range of weights not in a simple 10–18 pattern. The trio hydrogen, helium, lithium, beryllium covers weights around 1–9, not near 10–18. And carbon, nitrogen, oxygen, sulfur ends at sulfur with a weight around 32, not 18.