Explanation:

- Option 1: Delhi

- Delhi is known for its high literacy rate due to urbanization and better educational facilities. However, it's not the highest in the country.

- Option 2: Bihar

- Bihar has made improvements over the years, but it traditionally has a lower literacy rate compared to many other states.

- Option 3: Mizoram

- Mizoram has one of the highest literacy rates among the northeastern states but does not surpass Kerala.

- Option 4: Kerala

- Kerala consistently ranks as the state with the highest literacy rate in India, known for its educational initiatives and a strong focus on literacy.