The downward movement along the demand curve of a commodity is due to…

Changes in the demand of a commodity can be categorised into 2 categories: 

• Shift in the demand curve: When change in the demand is due to change in factors other than the own price of commodity.
• Movement along the demand curve: When change in demand is due to change in the own price of the commodity.

Shift in the demand has two types:

1. Increase in demand: When demand rises due to change in other factors like increase in income, favourable shift in tastes etc.
2. Decrease in demand: When demand falls due to change in other factors like decrease in income, unfavourable shift in tastes etc.

Movement along the demand curve has two types:

1. Extension of demand: When demand rises due to fall in the own price of the commodity
2. Contraction of demand: When demand falls due to rise in the own price of the commodity

In the above question, there is extension of the demand.