Answer:
The answer is b. Demand is unit elastic, and a decrease in price causes an increase in revenue
Explanation:
If a demand is unit elastic, any changes in price has no impact on the total revenue. Any changes in price will be balanced by any equivalent changes in quantity but in the opposite direction. So, revenue which is a product of price and quantity demanded will remain constant or unchanged that is ( i.e) there will be no change in revenue.
Take for example, if a price falls by 10%, demand increases by 10% and vice-versa, no change in total revenue as total revenue is a product of price and quantity.
The demand function will be PQ=K where P is price, Q is Quantity and K is a constant so any change in P is matched by Q so that product ( total revenue) remains the same as K
So with this explanation above option b is not possible