Pumice is derived from

Answer: (a) Volcanic rock

Pumice is a light, porous volcanic rock that can float.

The idea

A gas-rich melt can cool before its bubbles escape. The trapped bubbles leave many cavities and make the resulting rock unusually light. Distinguish this formation process from the broader rock family and the composition of its parent lava.

Gas-rich magma rises → Pressure drops and bubbles expand → Lava is expelled → Rapid cooling preserves bubbles → A highly porous volcanic rock forms

Why the others are wrong

(c) Igneous is correct in a broad sense, but “volcanic” is the precise answer.

(d) It forms from gas-rich (often acidic) lava — (a) is the broader answer the key picks.

The trap

Volcanic rocks are igneous — pick the most specific option.

Also know

Pumice is commonly produced by silica-rich explosive eruptions and may float until water fills its pores. Scoria is also full of cavities but is usually darker and denser. Obsidian is volcanic glass with few visible crystals; basalt is a common fine-grained volcanic rock. The options overlap because volcanic rock is a type of igneous rock.