In winter, in the industrialised and metro cities, especially in the morning hours, the visibility is greatly lowered due to the formation of a dark fog, generally resulting in serious road accidents. It also causes suffocation.
$(a)$ What does this indicate and also name this phenomenon?
$(b)$ How is this phenomenon produced? Name two gases which cause acid rain.

Differentiate between mixed cropping,intercropping,and crop rotation.

Two average students, Ram and Shyam, were discussing the following graphs in the class:
[Image: $1158-196$]
The question relating to the graphs was to identify which one of them was not possible. Ram and Shyam agreed that graphs $A, B$ and $C$ were not possible. But Shyam said that graph $D$ is possible, while Ram said that it is also not possible. Since their teacher was on leave, they could not ask her. Seeing this, Ratan, who was very intelligent, came to their rescue. He told Shyam that graph $D$ was also not possible.
$(a)$ Do you think that Ratan is right? If so, why is graph $D$ not possible?
$(b)$ What values are imbibed by Ratan?

The level of vitamins $A$ and $K$ is kept high in poultry feeds.

Vividha told Vasudha that she will show her some magic. Vividha took a metallic pipe. She asked Vasudha to hold one of its ends close to her ears. She gently tapped the other end of the pipe with a metallic object. She asked Vasudha what she heard. Vasudha said she heard two sounds.
$(a)$ Was this magic? Why did Vasudha hear two sounds?
$(b)$ What values are imbibed by Vividha?

What are the merits and demerits of fish culture?