Question

Pure water is:
A) Colourless and opaque
B) Colourless and transparent
C) Coloured and transparent
D) Colourless, odourless and transparent

Answer 1

An opaque substance doesn’t allow the light to pass through them and so it is not visible to the human eye, for instance, rock is an opaque object. And transparent substances are just the opposite, as it allows the human eye to see through it, as in the case of glass.

Complete step by step solution:
Pure water is the type of water which does not have any impurities in it. It is also called distilled water. Water can be purified by using a number of methods, where the removal of suspended solids, undesirable chemical, and biological impurities, along with gases from water is done. The main purpose of purifying water is to make it consumable for different purposes. Generally, water is purified, in order to make it drinkable for humans, as most of the water is infected it is not fit for use, but purification of water could also be done for a number of other known purposes, namely pharmacological, medical, industrial and chemical purposes. The physical methods which are used for purification of water include filtration, sedimentation followed by distillation, biological methods may include use of biologically activated carbon or slow sand filters, and for the chemical method, it includes chlorination and flocculation and sometimes the usage of electromagnetic radiation is also observed for the same purpose.
Purification of water could reduce the concentration of certain particles namely algae, fungi, parasites, suspended particles as well as bacteria and it could also reduce the concentration of a number of particles which are dissolved in the water.
Now if we consider the question, it asks some criteria which are fulfilled by pure water, and we have to choose the most appropriate option of all.
The first one says colourless and opaque, now we all know water is colourless but not opaque, meaning we can see through pure water, so it is transparent. And the first option is incorrect. Next option says colourless and transparent which are both correct, but we would still see the other option to make sure this one is the most appropriate one or not. Third option says coloured and transparent, which is not correct as water is not coloured. And the last option is colourless, odourless and transparent, now since we know that water is in fact odourless or it doesn’t have any specific odour, so this option would be the most appropriate one as it points out three of the properties of pure water.
So the correct option would be option D.

Note: Pure water is colourless as it doesn’t have any colour naturally. It is also odourless as it doesn’t have any specific odour and it is also transparent as we can see through pure water.