Given below are two statements: 
Assertion (A):  Pent-1-ene and pent-2-ene are position isomers.
Reason (R):  Position isomers differ in the position of a functional group or a substituent.

 

1. Both (A) and (R) are True and (R) is the correct explanation of (A).
2. Both (A) and (R) are True but (R) is not the correct explanation of (A).
3. (A) is True but (R) is False.
4. (A) is False but (R) is True.

Hint: The position of the double bond is different 
When two or more compounds differ in the position of substituent atom or functional group on the carbon skeleton then it is position isomerism. A double bond is a functional group whose position varies.
The structure is as follows:
 
C5H3-C4H2-C3H2-HC2=C1H2Pent-1-ene
C5H3-C4H2-HC3=C2H-C1H3Pent-2-ene
Hence, both assertion and reason are true and the reason is the correct explanation of assertion.