Final answer:
The rate of natural increase is 18 per 1,000.
Step-by-step explanation:
The rate of natural increase can be calculated by subtracting the crude death rate from the crude birth rate. In this case, the crude birth rate is 50 per 1,000 and the crude death rate is 32 per 1,000. So, the rate of natural increase is 50 - 32 = 18 per 1,000.
The answer is (a) 18 per 1,000.