Step 1 (Definition of compound wor(d).
A compound word is formed when two or more words are joined together to create a new word with a unique meaning.
Step 2 (Check each option).
(a) Elephant — Single word, not formed by joining two words.
(b) Classroom — Compound of "class" + "room", meaning a room where classes are held.
(c) Jumping — Single word formed from a verb + suffix "-ing", not a compound.
(d) Sunflower — Compound of "sun" + "flower", meaning a type of plant.
Step 3 (Conclusion).
"Classroom" and "Sunflower" are compound words. If only one answer is expected, the most common pick is "Classroom" in general tests, but technically both are valid compounds.
\[
{\text{Classroom (Option (b)}}
\]
\[
{\text{Sunflower (Option (d)}}
\]