Q6- What are weeds? How can we control them. (3 marks)
Q7- Give reasons for the following (4 marks)
(a) Aluminium foils are used to wrap food items.
(b)Immersion rods for heating liquids are made up of metallic substance.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Answers
Answer:
Explanation:
Ans.6- Weeds are unwanted wild plants that grow in the field. Weeds compete with the crop for nutrients, light, and space.
Some important weeding methods are:
†’ Weeds can be controlled using weedicides. It is a chemical, which is sprayed in the fields to kill all available weeds. Weedicides are not harmful to crops.
†’ Tilling before sowing of crops also helps in removing weeds. Tilling uproots the weeds. The best time for the removal of weeds is before they produce flowers and seeds.
†’ The manual method of removing weeds is with the help of a khurpi. It involves regular uprooting or cutting of weeds close to the ground.
Ans 7-(a) Aluminium is malleable, soft and does not react with food items, so it is used to wrap food items.
(b) Metals are good conductor of heat and electricity, so immersion rods are made up of metallic substances.
(c) Copper is less reactive than zinc, so it can not displace zinc from its salt solution.
(d) Sodium and Potassium are very reactive; they react with air and water, so they are stored in kerosene.