Bhetki,mullets,pearl spots and prawns are some of marine fish of high economic value.

Kanchan purchased gold from a jeweller. She was,however,very apprehensive about the purity of the gold purchased by her. Ultimately,she approached a person who claimed he could test its purity by making certain measurements of weight of the gold in air and water.
$(a)$ What principle was he making use of for testing purity?
$(b)$ Write the relation by which he found the relevant quantity.
$(c)$ What value did Kanchan imbibe?

Anil's father was getting late for a function which he had to attend with his family. He started driving very fast and very close to the vehicle in front of theirs. Anil told his father that he should not do so as in case of any emergency,an accident could occur. He explained this to his father in detail. His father got convinced and started driving within the permissible limit and maintained a good gap between his car and the vehicle ahead of him.
$(a)$ What might Anil have explained to his father to convince him?
$(b)$ What are the values shown by Anil?

In India,about $45 \%$ of the cultivated area is unirrigated,and scarce rainfall often causes crop failure,leading to drought-like conditions. This situation motivated villagers to use rainwater harvesting and watershed management.
$(i)$ What is meant by irrigation?
$(ii)$ List two different kinds of irrigation systems which can be adopted to supply water to agricultural land.
$(iii)$ What values does Rajan possess which helped villagers overcome their problem?

Farmer $X$ planted Soyabean $+$ Maize $+$ Cowpeas in the same field simultaneously in a set row pattern. Farmer $Y$ planted cereal crop in one season and leguminous plants in the next season on the same piece of land in pre-planned succession. $(a)$ Name the cropping patterns used by farmers $X$ and $Y$. $(b)$ State two advantages of the different cropping patterns followed by farmers $X$ and $Y$ respectively.

Write the modes by which insects affect the crop yield.