Explanation:

The correct preposition to use in this sentence is "in".

Reasoning:
The phrase "blind in one eye" is a common idiomatic expression used to describe someone who has lost their vision in one eye. It is the most appropriate phrase to use in this context because it accurately conveys the meaning that the mother-in-law is unable to see with one of her eyes.

Usage:
The preposition "in" is used in this sentence to indicate the specific body part that is affected by the blindness. It is commonly used in English to describe various physical conditions or characteristics of a person.

Example:
Here's an example sentence using the correct preposition:

- "My mother-in-law is blind in one eye, but she has excellent vision in her other eye."

In this sentence, the preposition "in" is used to show that the mother-in-law has lost her vision specifically in one of her eyes.

Other options:
Let's consider the other prepositions provided as options and explain why they are not correct:

- "From" is incorrect because it does not accurately describe the condition of being blind in one eye. It suggests that the mother-in-law is blind as a result of something or someone.

- "On" is incorrect because it does not convey the meaning of blindness in one eye. It suggests that something is physically covering the eye.

- "Of" is incorrect because it does not accurately describe the condition of being blind in one eye. It suggests that the mother-in-law is the possession of the blindness, rather than experiencing it.

The correct preposition to fill in the blank is "in". Here is a detailed explanation:
- The phrase "blind in one eye" is an idiomatic expression used to describe someone who is unable to see with one of their eyes.
- In this context, the preposition "in" is used to indicate the condition or state of being blind in a specific eye.
- The preposition "from" is not suitable in this context because it implies a sense of origin or source, which is not relevant to the sentence.
- The preposition "on" is also not appropriate because it implies being physically located on top of something, which does not convey the intended meaning in this sentence.
- The preposition "of" is not correct because it suggests possession or belonging, which is not the intended meaning in this sentence.
In summary, the correct preposition to complete the sentence is "in", as in "My Mother-in-law is blind in one eye."