Explanation:

- Canada is three times the size of India (1)______ its population is only about 26 million.

- The sentence contrasts Canada's large size with its relatively small population.

- Option:1, because - Implies causation, which doesn't fit the context here.

- Option:2, until - Suggests a point in time, which is incorrect for this context.

- Option:3, so - Implies a result, which is not appropriate here.

- Option:4, but - Correctly introduces a contrast between size and population.

- The average (2)______ of population is less than three persons per square kilometer (3)______ Canada.

- (2) indicates the word "density" correctly completes the context.

- (3) indicates a preposition like "in" fits the context.

- The distribution of population is highly (4)______.

- Suggests the word "uneven" or "skewed" completes the argument about population spread.

- Nearly 80 per cent of the people (5)______ in a narrow belt less than 300 kilometer wide along the southern border.

- (5) could be completed with the word "live" forming the logical conclusion to the statement.

Your selection of Option:4, but for blank No. 1 is correct.