pls tell question 3, 4 and 5

Answers
3. When an object is wholly or partially immersed in a fluid,it experiences an upthrust or loss in weight,which is equal to the weight of the water displaced by it.The force that causes the body to loose weight is called bouyant force or upthrust
or bouyancy.
Bouyancy or bouyant force acts against the original weight of the body that is immersed in the fluid.
4. The weight of the object is 10N,but it displaces 12N of water,thus the weight of the object is less than that of the weight of water displaced by it.Hence, the upthrust on the object will be more than its weight and hence it will float.
5.Ben's model boat weighed 4N,but it sank,as it must have displaced water whose weight is less than 4N,so the upthrust on the boat was not more than the weight of the boat,and hence the boat sank.