Step 1:
Advertising is a paid form of non-personal communication used to promote ideas, goods, or services.
Step 2:
A key feature of advertising is that the sponsor pays for media space or time.
Step 3:
• Assertion correctly defines advertising
• Reason correctly states that unpaid communication is not considered advertising
The reason properly explains the assertion.
Step 4:
Hence, the correct answer is:
\[
\boxed{\text{(1)}}
\]