How do you know something is dead

No vital signs

Vital signs include heart rate, respiratory rate, temperature and blood pressure

Is this without equipment?

Depending on what organism you are talking about, animals that can be seen with the unaided eye you can tell that they are dead by studying their bodily movements such as the rise or falling of their chest.

Plants with the unaided eye, the best  indicator is to take a branch or piece off and study the insides color, if it is green then mostly likely they are alive.

Now microscopic organisms are harder to say, it depends on what you are referring to.

c

explanation:

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.