Explanation:

Statement 1 is incorrect as Nuclear Fusion is source of sun’s energy not fission. (Hydrogen atoms fuse to form Helium)
Venus and not Mars is regarded as earth’s twin planet due to similar size, mass and density.
 
Even though mercury is the closest planet to sun, it is not the hottest. This is so because planets including our earth get heated not by incoming short wavelength solar radiation but by outgoing terrestrial radiation of long wavelength trapped by atmosphere. Due, to close proximity of mercury to the sun, the gases have escaped due to intense heat and solar winds and hence there is no atmosphere to trap the outgoing terrestrial radiation. Venus on the other hand has an atmosphere made up of primarily Carbon Di-oxide creating intense greenhouse effect and making Venus the hottest planet in the solar system.