Which of the following is a block mountain?

Answer: (b) Vosges

The Vosges (and Black Forest) are block mountains either side of the Rhine rift.

The idea

Faulting can leave one crustal block higher than neighbouring blocks without folding it into a mountain chain. The raised block is a horst; the lowered trough is a graben. Identify the mountain by its structural origin rather than height.

Crust is stretched → Parallel faults develop → Blocks move relative to one another → A central trough sinks → Flanking blocks remain relatively high → Block mountains border a rift valley

Why the others are wrong

(a) The Alps are fold mountains.

(c) The Rockies are fold mountains.

(d) The Andes are fold mountains.

Elimination technique

Group the Alps, Rockies and Andes as fold-mountain examples. The remaining option, Vosges, belongs to the horst-and-graben setting of the Rhine valley.

Also know

The Vosges in France and the Black Forest in Germany flank the Upper Rhine graben. The Alps, Rockies and Andes are commonly taught as fold-mountain examples, though real mountain belts also contain faults. A residual mountain is an erosion remnant; a volcanic mountain is built by erupted material.