Answer:
C.
Step-by-step explanation:
Stereoisomers are molecules that have the same molecular formula and with their atoms connected in the same way but pointing in different directions.
cis-Pent-2-ene has formula C₅H₁₀
A. is wrong, because its formula is C₅H₁₂
B. and D. are wrong, because their formulas are C₅H₈
The only option left is C. It has formula C₅H₁₀
C. is a stereoisomer of cis-pent-2-ene, because atoms 1 and 4 are on opposite sides of the double bond.
Think of the C=C bond as a river.
In the cis isomer (top), atoms 1 and 4 are on the same side of the river (zis = zame zide).
In the trans isomer (bottom), atoms 1 and 4 are on opposite sides of the river (trans = across or opposite).
So, C. is a stereoisomer of cis-pent-2-ene.