1586: Urea is prepared by the chemical reaction of:
(a) Ammonia and Carbon dioxide
(b) Ammonium sulphate and calcium chloride
(c) Acetamide and ethyl alcohol
(d) Chlorine and water
1587: Within biological communities, some species are important in determining the ability of a large number of other species to persist in the community. Such species are called
(a) Keystone species
(b) Allopatric species
(c) Sympatric species
(d) Threatened species
1588: Assertion (A) :
Activated charcoal is used for decolourising sugar solution.
Reason (R) :
Activated charcoal absorbs the impurities on its surface.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not a correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
1589: Consider the following statements:
1. The Earth's magnetic field has reversed every few hundred thousand years.
2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
3. When living organisms originated, they modified the early atmosphere of the Earth.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
1590: A bus is moving with a speed of 30 km/hr ahead of a car with a speed of 50 km/hr. How many kilometers apart are they if it takes 15 minutes for the car to catch up with the bus ?
(a) 5 km
(b) 7.5 km
(c) 12.5 km
(d) 15 km