(a) When the cold spell will take place, then the demand for gas will increase because of which the demand curve for gas will shift out or to the right. So, when the cold increases, the demand for heaters will increase because of which more gas will be required by the electric power plants. The final impact will be that the equilibrium price as well as equilibrium quantity of gas will rise.

(b) When the National grid instructs the major gas users to reduce their demand, then the demand will fall and because of which the demand curve will shift inside but the magnitude by which the demand decreases cannot be known (whether it is equal, less or more than the previous increase in demand).

(c) Two other factors which can impact the demand of gas are : the regulation by government and changes in the price of other alternative or substitutes of gas. If government imposes a subsidy on gas or imposes any tax of gas, then it can either increase or decrease the demand for gas. When the substitutes of gas become relatively cheaper, then the demand for gas will decrease (as gas is more expensive in comparison) and when the substitutes of gas become more expensive, then the demand for gas will increase as gas will be the relatively cheaper alternative.

(d) Price elasticity of demand is defined as the amount by which the quantity demanded of any good changes due to one percent change in the price of the good. Thus, for gas, the demand will be relatively price inelastic as there are a very small number of easily available close substitutes . Thus, any increase in the price of gas will amount to only a very small change in quantity demanded of gas.