Combine the sentences with a suitable conjunction:
Mohan is honest. He is sincere. (both-and)

Hint: ‘Both’ is paired with ‘and’ to add emphasis to two coordinated elements in a sentence. This means that you have to use both of the conjunctions in the given sentence.

Complete answer:
‘Both’ is a focusing adverb and ‘and’ is a coordinator for addition. This paired expression is also called a "correlative conjunction”.
As suggested by their name, correlative conjunctions correlate, working in pairs to join phrases or words that carry equal importance within a sentence. For example, “neither/nor”, “either/or”, and “both/and”.
They can be used in a sentence in the following way:
I will either go for a hike or stay home and watch TV.
Jerry is neither rich nor famous.

This is how to use ‘both/and’ in a sentence:
She is both intelligent and beautiful.

In this sentence, you can see that these conjunctions are separate. This means that there are pre-determined placements for these words, which are considered grammatically appropriate. Let us deconstruct the above sentence:
The sentence above is combining the two sentences ‘She is intelligent’ and ‘She is beautiful’. It used the correlative conjunctions to do so. The word ‘both’ is placed before the first adjective. This is the grammatically correct placement of that word. Then, the word ‘and’ goes between the two adjectives. This is always the placement of ‘and’ in case of two adjectives.

Now, we can apply this same rule to the given sentences.
In the given sentences, there are two adjectives - honest, sincere. When we have two adjectives, the word ‘both’ goes before the first adjective, and the word ‘and’ goes between the two adjectives. This means that the phrase will be ‘both honest and sincere’. The verb and subject will not change.

So, the correct answer is ‘Mohan is both honest and sincere’.

Note:
Figure out the situation in which you use both the given conjunctions. This will help you to understand which one to use where. Then, identify the correct placing of the given conjunctions, and write the correct answer.