A scientist needs to check several parameters before coming
to a conclusion about the amount of water pollution. The scientists needs to
check the amount of dissolved oxygen in the water, temperature of the water,
the clarity of the water, the PH level of the water and also the amount of
bacteria present in the water. There may be other criteria’s, but the mentioned
ones are enough to gauge the amount of pollution in the water. Scientists often
takes fish and aquatic plants from the water to be tested to check the amount
of pollution indirectly affecting these species.
Sun isn't actually planet but star. Really big ball made of gases. Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%). Sun is the biggest object in our Solar System. It's 99.86% of the total mass of the Solar System.
... wikipedia is really grat if you have questions like that ;)
