The correct answer is option 1 - Dhanush is a customized and naval variant of the Prithvi missile.

To further explain the options, option 2 states that Dhanush has a range of 700 km. This means that the missile can be launched and accurately hit targets that are up to 700 km away.

Option 3 states that Dhanush can be launched from an aircraft. However, this is incorrect. Dhanush is a surface-to-surface ballistic missile that is launched from naval ships, specifically from naval warships.

Option 4 states that Dhanush cannot carry nuclear warheads. While Dhanush is not specifically designed to carry nuclear warheads, it has the capability to be armed with both conventional and nuclear warheads, depending on the mission requirements.

In summary, the correct answer is option 1 because Dhanush is a customized and naval variant of the Prithvi missile, and it is primarily launched from naval warships.