The correct answer is option 1: Both the statements are individually true and statement II is the correct explanation of statement I.

Statement I states that sound waves cannot propagate in a vacuum, which is true. Sound waves are mechanical waves that require a medium, such as air, water, or any other substance, to travel through. In a vacuum, there is no medium for sound waves to propagate, so they cannot be transmitted.

Statement II states that sound waves are elastic waves and require a medium to propagate, which is also true. Elastic waves are waves that involve the displacement and restoration of particles in a medium. Sound waves are a type of elastic wave, as they involve the compression and rarefaction of particles in a medium, causing the disturbance to propagate as a wave. Therefore, statement II provides a correct explanation for why sound waves cannot propagate in a vacuum.

In summary, both statements are true, and statement II correctly explains why sound waves cannot propagate in a vacuum.