641. Three elements needed for the healthy growth of plants are_________________?
A. N P K
B. N K C
C. N S P
D. N Ca P

642. Residence time of methane in the atmosphere is___________________?
A. 3 – 7 days
B. 2 -3 days
C. 3 – 7 years
D. 2 – 3 years

643. Hypochlorous acid is used for disinfecting the water it reacts with the dissolved ammonia producing___________________?
A. NH2Cl
B. NHCI2
C. NCI2
D. all of the above

644. Acid present in acid rain may be__________________?
A. H2SO4
B. HNO3
C. both A and B
D. none

645. Which of the following is not a condition for the formation of smog ?
A. sufficient NO
B. sunlight
C. less movement of air
D. winds

646. In which of the following layer of atmosphere there is more thickness of ozone layer ?
A. troposphere
B. stratosphere
C. mesosphere
D. photosphere

647. Which of the following air pollutants is more dangerous for ozone layer ?
A. CFC
B. CO2
C. CO
D. Oxides of nitrogen

648. Which statement is wrong ?
A. the amount of ozone layer is greater in the region close to the equator
B. ozone acts as filter for UV radiations
C. in the equatorial region it acts as pollutant
D. CFCs play effective role in removing O3 in the stratosphere

649. In the purification of portable water the coagulant used is_________________?
A. alum
B. nickel sulphate
C. copper sulphate
D. barium sulphate

650. Newspaper can be recycled again and again how many times ?
A. 2
B. 3
C. 4
D. 5