The correct answer is option 1, hand.

Involuntary muscles are muscles that are not under conscious control. They contract and relax without us having to think about it. These muscles are also called smooth muscles. Examples of involuntary muscles include the muscles in our internal organs, such as the heart, intestines, and stomach.

The heart is made up of involuntary muscles, which allow it to beat and pump blood throughout the body. These muscles are automatically regulated by the autonomic nervous system and do not require conscious effort to function.

Similarly, the muscles in the walls of the intestine and stomach are also involuntary. They work to move food through the digestive system, contract to mix and break down food, and push it along for absorption. These actions occur without us having to consciously think about them.

On the other hand, the hand primarily contains voluntary muscles, also called skeletal muscles. These are the muscles that we can consciously control to perform various movements and actions. Examples of voluntary muscles in the hand include those responsible for gripping, grabbing, and releasing objects.

Therefore, the correct answer is option 1, as the hand does not contain involuntary muscles.