436: Strips of two metals A and B are firmly joined together as shown in the figure.
Explanation:
On heating a double striped metal made up of two different metals and if the metal which expands more will be at top and the metal which expands less remains at bottom, then it curves downwards and assumes an inverted 'U' shape.
437: Which one of the following sets of elements was primarily responsible for the origin of life on the Earth?
(a) Hydrogen, Oxygen, Sodium
(b) Carbon, Hydrogen, Nitrogen
(c) Oxygen, Calcium, Phosphorus
(d) Carbon, Hydrogen, Potassium
Explanation:
The correct answer of this question is:
(b) Carbon, Hydrogen, Nitrogen
438: Which one of the following agricultural practices is eco-friendly ?
(a) Organic farming
(b) Shifting cultivation
(c) Cultivation of high-yielding varieties
(d) Growing plants in glass-houses
Explanation:
Organic farming is also called eco farming, where the Minimum or no use of chemicals like pesticides, fertilizers, growth regulators etc, is practiced in the agricultural production activities which are replaced by the increased usage of biopesticides, biofertilizers, organic manures etc. which will affect least to the surrounding environment.
439: The type of crop which is able to fix nitrogen from air is known as:
(a) Tuber
(b) Coffee
(c) Legume
(d) Wheat
440: Which of the following is a weedkiller?
(a) Insecticide
(b) Methyl salicylate
(c) Heribicide
(d) None of these