Fill in the blanks with the most appropriate option:-

He is true …… his word.

To

The correct option to fill in the blanks is to.

The sentence is about someone who is honest and reliable. The preposition "to" is used to indicate loyalty or faithfulness. It is the most appropriate preposition to use in this context, as it describes the person's commitment to their word.

The other options are not as appropriate:

• By can be used to indicate means or method, but it is not as appropriate as "to", as it does not convey the same sense of loyalty or faithfulness.
• For can be used to indicate purpose or reason, but it is not as appropriate as "to", as it does not convey the same sense of commitment or dedication.
• At can be used to indicate a location, but it is not as appropriate as "to", as it does not convey the same sense of loyalty or faithfulness.