The correct answer is: A. number of payment periods.
In the calculation of time value of money, $N$ represents the number of payment periods. This is the number of times that a payment is made over the course of the loan or investment. For example, if a loan is for 5 years and the payments are made monthly, then $N=60$.
The other options are incorrect because they do not represent the number of payment periods. Option B, number of investments, is incorrect because it does not take into account the number of times that a payment is made. Option C, number of instalments, is incorrect because it is a synonym for payment periods. Option D, number of premium received, is incorrect because it is a term used in insurance, not in the calculation of time value of money.