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IIT JEE 2006 Sample Question Paper

Passage 7

Several methods were investigated to reduce pollution emissions from a steel mill smokestack. Steel is mostly iron (Fe), but it also contains carbon (C). Impurities containing sulfur (S), nitrogen (N), or phosphorus (P) form gaseous compounds with oxygen that become pollutants. The smoke contains these pollutants and also tiny dust particles that pollute the air, are blown around by the wind, and eventually fall to the ground.

Method 1
Steel mill smoke was passed across a set of electrified plates in the smokestack. The electrified plates attracted the dust particles in the smoke and removed them from the emissions. The efficiency of dust particle removal, which is dependent on the size of the particles, is shown in Table 1.

Table 1.
Voltage on plates
Particles removed

Method 2
The smoke was passed through filters of different pore size in the smokestack that trapped dust particles and also decreased the amount of smoke leaving the stack. The data are shown in

Table 2.
Filter pore size
Particles trapped
Amount of time for filters to drop to 50% efficiency

Method 3
To reduce pollution by chemical means, the smokestack emissions were bubbled through solutions of concentrated alkali (solutions of OH- ions). Table 3 shows the percent of the 3 pollutants removed versus the alkali concentration.

Table 3.
Alkali concentration

Q. 33 If the plant's smoke contained equal amounts of S, N, and P, which of the following alkali concentrations would remove the most total pollution?

  1. 1%
  2. 3%
  3. 5%
  4. 10%

Q. 34 Which of the following statements about the alkali concentration is consistent with the results of Method 3?

  1. A higher alkali concentration results in more P removed.
  2. A higher alkali concentration results in more S removed.
  3. A lower alkali concentration requires more filters to remove dust particles.
  4. A lower alkali concentration results in an increased time required to remove all of the chemical pollutants

Q. 35 Based on the characteristics of the filters used in Method 2, which of the following best describes the practical problem involved in choosing the best type of smokestack filter? The filter that traps the highest percentage of particles:

  1. requires the highest voltage across the electrified plates.
  2. reacts with alkali solutions.
  3. needs to be replaced least often.
  4. needs to be replaced most often.

Q. 36 If the smokestack of the steel mill was doubled in height, what effect, if any, would this be expected to have on the removal of pollutants?

  1. Filter efficiency would decrease because dust particles could more easily fall back down the stack.
  2. Electrostatic plate efficiency would increase because voltage increases with height.
  3. Dust particles would accumulate into larger pieces and would be more easily removed from the smoke.
  4. It cannot be determined from the given information.

Q. 37 Which of the following assumptions about reducing pollution emissions is common to both Methods 1 and 2 ?

  1. Emissions can only be removed by filters.
  2. Emissions can only be removed by electrified plates.
  3. Emissions must be captured in the smokestack to be removed.
  4. Emissions must be captured after they leave the smokestack.

Q. 38 To further investigate the effects of voltage on the removal of dust particles from steel mill smoke, the scientists could use which of the following procedures?

  1. Determining where the particulate matter falls to the ground after leaving the smokestack
  2. Determining what sizes of particles are removed from the smoke at different voltages
  3. Determining how the filters react when an alkali solution is passed through them
  4. Determining how the filters react when an acid solution is passed through them
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