Answer:
According to Le-chatelier principle, equilibrium will shift towards left to minimize concentration of 
and keep same equilibrium constant
Explanation:
In this buffer following equilibrium exists -
So, is involved in the above equilibrium.
When a strong base is added to this buffer, then concentration of increases. Hence, according to Le-chatelier principle, above equilibrium will shift towards left to minimize concentration of and keep same equilibrium constant.
Therefore excess amount of combines with 
to produce ammonia and water. So, effect of addition of strong base on pH of buffer gets minimized.
The correct answer is option B. Dirty water is a mixture of solid particles and liquid. It is both a mixture and pure substance.
The dirty water sample has both gravel and liquid water in it. After filtration the gravel is removed so the water sample looks clearer than before filtration. Liquid water is a pure substance because it is a compound that is made up of elements hydrogen and oxygen. Now the gravel is only physically combined with the liquid water, thus giving the water sample properties of a mixture. And like any mixture, gravel is physically separated through filtration from the liquid water.
Thus the water sample of the chemists is both a mixture and pure substance.
Heat energy is required.
In distillation, the solution is first heated, where heat energy is required, such as using a bunsen burner.
When the solution is heated, the water may reach its boiling point and evaporate. However, salt does not. When water molecules evaporates, it travels through a condenser that cools it down into liquid again. Therefore we get pure water. Salt is also obtained in the original beaker.
Therefore to first start this process, heat energy is required.
