Explanation:

Sentence I. A country like India, the children of which are living in poor conditions, should avoid raising fancy slogans.
The original sentence just expresses the ironic situation of street children in India and it nowhere suggests an idea. Usage of ‘should’ in the sentence thus makes the sentence I a weak choice.
Sentence II. India with as big a child population as 3 million must work towards improving its children’s life conditions instead of raising slogans.
The sentence above is factually incorrect as it states the total population of children in India as 3 million where it’s just the population of street children in the country.
Sentence IV. On one hand India sees future in its children the population of which are as big in size as 3 million, it, on the other hand, neglects many of them who are living in extreme conditions.
The sentence III is incorrect as well following the same logic as discussed for the sentence II.
Sentence V. Being a country with 3 million street children, India must not raise slogans which are self-derogatory.
The sentence above is absolutely absurd and makes no sense at all.
Sentence III. It’s ironic to see India as a country that takes pride in proclaiming its children as the future of the nation whereas a huge population of them is living in abject conditions.
The sentence above appropriately conveys the same meaning as the original sentence does.
Option C is hence the correct answer.