When a glass rod is placed in steam, its length increasesbut its width :

The correct answer is (a). When a glass rod is placed in steam, its length increases because the glass expands when heated. However, the width of the rod does not change because the glass expands uniformly in all directions.

Option (b) is incorrect because the width of the rod does not decrease. Option (c) is incorrect because the width of the rod does not increase. Option (d) is incorrect because the width of the rod does not become irregular.