**Explanation:**

The correct answer is option 'B', which states that X can enter into a contract during intervals when he is of sound mind.

Here is the detailed explanation:

**Interval of Sound Mind:**
- The term "interval of sound mind" refers to the periods when X is not experiencing any unsoundness of mind and is capable of understanding the nature and consequences of his actions.
- During these intervals, X has the ability to comprehend and make rational decisions, including entering into contracts.

**Legal Capacity to Enter into Contracts:**
- In order to enter into a valid contract, a person must have the legal capacity to do so.
- Legal capacity refers to a person's ability to understand and be bound by the terms of a contract.
- A person who is of unsound mind generally lacks the legal capacity to enter into contracts.

**Unsoundness of Mind:**
- X, as a patient in a lunatic asylum, is presumed to have periods of unsoundness of mind.
- During these periods, X may lack the ability to understand the nature and consequences of his actions, including entering into contracts.
- Therefore, X cannot enter into a contract during the course of his unsoundness of mind (option 'C').

**Discharged but of Unsound Mind:**
- X may be discharged from the lunatic asylum but still be of unsound mind.
- In such a situation, X would still lack the legal capacity to enter into contracts.
- Therefore, X cannot enter into a contract when he is discharged but of unsound mind (option 'D').

**Intervals of Sound Mind:**
- The only option that remains is option 'B', which states that X can enter into a contract during intervals when he is of sound mind.
- During these intervals, X has the legal capacity to understand and be bound by the terms of a contract.
- It is important to note that the validity of the contract may be subject to further examination to ensure that X was indeed of sound mind at the time of entering into the contract.

In conclusion, X can enter into a contract during intervals when he is of sound mind. It is essential to consider the periods of soundness and unsoundness of mind when determining the legal capacity to enter into contracts for individuals in a lunatic asylum.