If minimum subscription is not received, the whole amount collected has to be refunded within how many days of the end of subscription?

Correct option is B

As per SEBI Guidelines and the Companies Act provisions relating to the issue of shares to the public, a company must receive at least 90% of the minimum subscription (including underwriting) within 60 days from the date of issue.
If minimum subscription is not received, then:
All application money must be refunded within 30 days from the closure of the subscription list.
If the company fails to do so, it must pay interest @ 15% per annum on the delayed refund.
Thus, the correct answer is: Option (b) 30 days.