Heat is required to change 1 kg of ice of –20ºC into steam. Q1 is the heat needed to warm the ice from –20ºC to 0ºC, Q2 is the heat needed to melt the ice, Q3 is the heat needed to warm the water from 0ºC to 100ºC and Q4 is the heat needed to vaporize the water. Then
(a) Q4 > Q3 > Q2 > Q1
(b) Q4 > Q3 > Q1 > Q2
(c) Q4 > Q2 > Q3 > Q1
(d) Q4 > Q2 > Q1 > Q3
