3. A compound formed of CO2 and water is sour? Why?

Explanation:

it's because when CO₂ reacts with H₂O then it forms H₂CO₃ (carbonic acid), which is a acid that's why a compound formed by CO₂ and H₂O is sour.

Reaction:

CO₂ + H₂O → H₂CO₃

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.