(a) Individual demand refers to the quantity of a commodity that a consumer is willing and able to buy, at different possible prices during a specific period of time.
On the other hand, Market Demand refers to the quantity of a commodity that all consumers are willing and able to buy, at each possible price during a specific period of time.
Market demand is horizontal summation of all the individual demands.
Factors affecting demand for a good by an individual are :-
(b) (i) When the quantity demanded changes due to a change in own price of the commodity, keeping other factors constant, it is known as change in quantity demanded whereas when the demand changes due to a change in other factors other than the price of the commodity, it is known as change in demand.
(ii) Change in quantity demanded leads to a movement along the demand curve whereas change in demand leads to a shift in the demand curve.