Consider the following statements.
Other things remaining unchanged, market demand for a good might increase if
1. Price of its substitute increases.
2. Price of its complement increases.
3. The good is an inferior good and income of the consumers increases.
4. Its price falls.
Which of the above statements are correct?

The correct option is 1 and 4 only.

To determine which factors cause an increase in the market demand for a good, let us analyze each statement individually based on standard microeconomic principles:

1. Price of its substitute increases:
Substitute goods are items that can be used in place of one another (for example, tea and coffee). When the price of a substitute good increases, consumers switch away from that substitute and buy more of the given good instead. As a result, the market demand for the given good increases. Therefore, Statement 1 is correct.

2. Price of its complement increases:
Complementary goods are consumed together (for example, cars and petrol). When the price of a complementary good increases, consuming the pair becomes more expensive overall. Consequently, the demand for both the complementary good and the given good decreases. Therefore, Statement 2 is incorrect.

3. The good is an inferior good and income of the consumers increases:
An inferior good is a good for which demand decreases as consumer income increases, because consumers replace it with higher-quality substitutes (superior or normal goods). Therefore, if income increases, demand for an inferior good will decrease, not increase. Hence, Statement 3 is incorrect.

4. Its price falls:
According to the Law of Demand, when the price of a good falls (ceteris paribus / other things remaining unchanged), consumers buy a larger quantity of that good. This leads to an increase in demand / quantity demanded for the good. Therefore, Statement 4 is correct.

Conclusion:
Statements 1 and 4 are correct, making 1 and 4 only the correct answer choice.