300. Which of the toxic heavy metals is found in modern tannery industries? [CPO SI 2011]
     (a) Nickel
     (b) Zinc
     (c) Chromium
     (d) Lead
Ans: (c)
301. Which of the following contains high content of lead? [CPO SI 2011]
     (a) Coal
     (b) Cooking gas
     (c) High octane fuel
     (d) Low octane fuel
Ans: (c)
302. Cooking gas is a mixture of [CPO SI 2010]
     (a) methane and ethylene
     (b) carbon dioxide and oxygen
     (c) butane and propane
     (d) carbon monoxide and carbon dioxide
Ans: (c)
303. Two elements which are used to absorb neutrons to control the chain reaction during nuclear fission are [CPO SI 2010]
     (a) Boron and Cadmium
     (b) Boron and Plutonium
     (c) Cadmium and Uranium
     (d) Uranium and Boron
Ans: (a)
304. The most commonly used chemicals in the artificial rain making or cloud seeding are [CPO SI 2010]
     (a) Silver Iodide (Agl)
     (b) Sodium Chloride (NaCl)
     (c) Dry Ice (Frozen CO2)
     (d) All of the above
Ans: (a)
305. Consider the following:
     1) Carbon dioxide
     2) Oxides of Nitrogen
     3) Oxides of Sulphur
     Which of the above is/are the emission/emissions from coal combustion at thermal power plants? [CSAT 2011]
     (a)  1only
     (b)  2 and 3 only
     (c)  1 and 3 only
     (d)  1, 2 and 3
Ans: (d)
306. Silver ware turns black after a period of time due to formation of: [NDA 2011]
     (a) nitrate coating on silver .
     (b) sulphide coating on silver
     (c) chloride coating on silver