If you'r referring to some objects, it means that the mass of the object is less than the water so it floats. If the mass of an object is greater than the mass of the water, it will sink. Compare it to a balloon, helium makes it rise, while normal air makes it sink.
Answer:
C
Explanation:
becauase i just tooke the test
B is you answer sorry i dont quite know how to explain it in a way that you and anybody else would understand it.
Answer:d
Explanation:
Suppose V is the voltage of battery and R is the resistance of bulb
so Power drop for initial stage

When another identical bulb of same resistance is applied in parallel so voltage Drop across both the resistor will be same i.e. V
so Power consumed 
so there is no change in power and hence no dip in brightness