Here is the answer
a) The images used to describe these slums are:
1.Slag heap
2.Foggy slum
3. Bottle bits on stone, and
4.slums as big as doom
These images convey the miserable lives of the poor children, their dirty and unhygienic surroundings which is not less than hell.
b) These children live in a very small cell like rooms with unhygienic surroundings. Their life is filled with darkness and hopelessness. They live in poverty, foggy surroundings, disease, no essential of life etc. which is not less than a hell.
c) The figure of speeches used in the last line are :
Similie:(Slum as big as doom)
Pun: (maps: figurative meaning is the life of the children and subjective meaning is the area in which they live)