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The correct answer is (a) PbSe

For EXPLANATION I WOULD say: PbSe is USED as detector in improved infrared ANALYZER used for gas ANALYSIS. It is a solid state detector.

Right CHOICE is (a) It will cause a net downward FLOW

The best I can explain: In analyzers based on gas density, if the SAMPLE CARRIES a gas having a higher density than the detector it will cause a net downward flow. It will obstruct flow in the lower path.

Correct choice is (a) True

The BEST explanation: In Paramagnetic oxygen analyzer, when no oxygen is present the magnetic force balances TORQUE of the fibre. If oxygen is present, it WOULD DISPLACE the dumb-bell sphere.

Right CHOICE is (a) Thermo-magnetic analyzers

Explanation: Magnetic wind analyzers are also KNOWN as Thermo-magnetic analyzers. In Europe, it is known as Magnetic wind analyzers. In the UNITED STATES, it is known as Thermo-magnetic analyzers.

Right answer is (c) Oxidation-reduction reaction

The explanation: In ELECTROCHEMICAL cells, an oxidation-reduction reaction OCCURS in the presence of HYDROGEN sulphide. A current starts FLOWING and it is proportional to the CONCENTRATION of hydrogen sulphide.

Correct option is (a) Treating sample GAS with pressurized oxygen

The best I can EXPLAIN: NO is converted into NO2 for ANALYSIS in UV and Visible ANALYZERS by treating sample gas with pressurized oxygen. This is because direct measurement of NO is not possible using UV and Visible analyzers.

The correct choice is (b) By adjusting the needle VALVE

Explanation: NITROGEN can be CALIBRATED for dry gases by adjusting the needle valve. In this way, the ERROR will be compensated.

Right choice is (c) 40-60 cc/min

The BEST I can explain: In the Beckman instrument, the flow rate recommended when the SAMPLE enters directly for rapid RESPONSE is 40-60 cc/min. paramagnetic OXYGEN analyzer was first described by Pauling.

Correct choice is (a) True

For explanation I WOULD say: HYDROCARBONS NEED to be removed from the sample gas to avoid errors. This is because they may react on the HEATED filaments and lead to a change in temperature and resistance.

The correct CHOICE is (C) When all but one component have same thermal conductivities

The best explanation: When all but one component have the same thermal conductivities, thermal conductivity ANALYZER can be used for multi-component mixtures. The MIXTURE is then treated as a BINARY mixture.

The CORRECT option is (b) SLOW response

Explanation: Thermistors have fast response.They are arranged as HEAT sensing ELEMENTS in the Wheatstone BRIDGE.

Right choice is (d) THERMOMETER

For explanation: Thermometer is not used as a detector in analyzers BASED on GAS density. Thermistors and HOT wires are GENERALLY used.

Right answer is (b) TREATING sample gas with ozone

Easy explanation: NO is converted to NO2 for analysis in CHEMILUMINESCENT analyser by treating sample gas with ozone.

NO + O3 —>NO2 + O2

Right OPTION is (C) 1ppb to 1000PPB

For explanation: The instruments based on chemiluminescence maintain linearity between 1ppb to 1000ppb. These are used to measure NO in exhaust GASES in vehicles.

The correct ANSWER is (b) Dry air

Explanation: If the oxygen content is not greater than 21%, dry air is USED to set the SPAN point. This is done for calibration purposes.

Right option is (c) HYDROGEN

The best I can EXPLAIN: Hydrogen has the HIGHEST thermal conductivity. Chlorine has the lowest thermal conductivity in the LIST.

Correct answer is (a) True

Easiest explanation: Changes in the COMPOSITION of gas stream give rise to changes in thermal CONDUCTIVITY of the gas stream. This principle is USED in thermal conductivity ANALYZERS.

Correct option is (d) Redox reactions

To explain I would say: Polarographic cells type of electrochemical METHOD USES redox reactions. It is USED to measure the partial pressure of the PERCENTAGE of oxygen.

Correct answer is (d) It is transparent in UV visible regions

For EXPLANATION I WOULD say: Nitrogen oxide cannot be directly analysed using UV and Visible ANALYZERS because it is transparent in UV visible regions. HENCE, it is converted into nitrogen dioxide and then analysed.

The correct option is (c) Narrow bandpass FILTER

To explain I would SAY: The filter is used in an improved VERSION of infrared gas ANALYZER at the output end is narrow bandpass filter. The bandpass characteristics are matched with the absorption SPECTRA of the gas of interest.

The correct choice is (d) Gas-DENSITY difference between both the DETECTORS

To explain I would say: In analyzers based on gas density, the unbalance of the bridge is LINEARLY PROPORTIONAL to a gas-density difference between both the detectors. Instruments based on the PRINCIPLE of gas-density balance are commercially available.

Right choice is (d) By using a photospectrometer where a GAS sample is analysed and detected with a photocell

To EXPLAIN: By using a photospectrometer gas sample is analysed, for MEASURING nitrogen. It is then selectively FILTERED by using a photocell which provides an appropriate electric signal.

Right option is (a) Platinum-iridium

For explanation: To IMPROVE PARAMAGNETIC oxygen analyzer, the quartz suspension MUST be REPLACED with Platinum-iridium. It is more ROBUST.

Right option is (B) False

To explain I would say: The EXTREMELY low inertia of the thin membrane in the oxygen sensor allows it to ATTAIN EQUILIBRIUM. It reaches an equilibrium STATE in 0.25 to 0.5 seconds.

The correct option is (c) With SUFFICIENT electrical EXCITATION and at suitable pressures

For explanation: Gases emit radiation with sufficient electrical excitation and at suitable pressures. Gases emit radiation in different ways. It can be in the form of spark, ARC or GLOW DISCHARGE in different parts of the radiation spectrum.

The CORRECT option is (b) False

Explanation: Polarographic cells are not used to measure the partial PRESSURE of gases in static gas monitoring SYSTEMS alone. They can ALSO be used for measuring the partial pressure of gases in continuous samples and INJECTED samples.

Correct ANSWER is (b) Lead Sulphide, BROWN colour

For EXPLANATION I would say: HYDROGEN Sulphide REACTS with Lead Acetate to form Lead Sulphide which is brown in colour. Hydrogen acetate in other words is acetic acid and is colourless.

The correct choice is (a) COLLISIONAL de-excitation

For explanation I WOULD say: The molecules return to the GROUND STATE by collisional de-excitation. This results in an increase in temperature.

Right choice is (a) True

To EXPLAIN: Nitrogen DIOXIDE can be detected with a paramagnetic analyser. This is because nitrogen has paramagnetic PROPERTY IE. it is attracted by magnetic fields.

Correct option is (b) Gas PERMEABLE MEMBRANE

For explanation: The UNMARKED component is gas permeable membrane. Electrochemical CELL is an electrochemical gas diffusion sensor.

The correct answer is (a) True

Easiest explanation: VIBRATION excitation occurs only if the SAMPLE has hetero-atomic molecules. Hence, infrared analyzers are not used for GASES WHOSE molecules are FORMED by two identical atoms.

The correct answer is (b) False

The best EXPLANATION: When hot-wires are used as detectors amplification is REQUIRED. The AMPLIFIED SIGNAL is given to the recorder.

Right choice is (b) With the help of the needle valve

Explanation: SAMPLE rates of nitrogen meter can be ADJUSTED with the help of a needle valve. Modern nitrogen ANALYZERS have digital DISPLAYS.

The correct answer is (a) True

Best explanation: The LIGHT OUTPUT from the discharge TUBE is interrupted by means of a ROTATING slotted disc. Hence, a chopped output is obtained.

The correct option is (d) Difference between magnetic SUSCEPTIBILITY of SPHERE and that of surrounding gas

The explanation is: The PARAMAGNETIC property of oxygen is used in this method for the analysis of oxygen. The force produced during operation of Paramagnetic oxygen analyzer is PROPORTIONAL to the difference between magnetic susceptibility of sphere and that of surrounding gas.

The correct choice is (B) 50-250 cc/min

To explain: In the Beckman instrument, the flow rate recommended when the sample enters through a porous diffusion DISC is 50-250 cc/min. PARAMAGNETIC oxygen analyzer was FIRST DESCRIBED by Pauling.

Correct choice is (d) WHEATSTONE BRIDGE becomes BALANCED due to TEMPERATURE change

Explanation: In Hartman and Braun oxygen analyzer, the magnetic wind COOLS the heated winding. As a result, the bridge becomes unbalanced.

The correct choice is (c) INERT gases

The EXPLANATION: In calibration of CO2 analyser, in order to establish ZERO calibration inert gases are used as sample. Generally, room AIR is also used.

Correct answer is (c) One VANE should be at HIGHER potential than the test body and the other vane should be at lower potential

To EXPLAIN I would say: In Paramagnetic oxygen analyzer, the two CHARGED vanes should be such that one vane should be at higher potential than the test body and the other vane should be at lower potential. This electric FIELD produces a force.

Correct CHOICE is (d) Ambient air

The explanation: In OXYMAT-M oxygen analyser, ambient air is usually used as a REFERENCE gas. Its measuring PROCEDURE is based on PRESSURE difference which DEVELOPS between two gases having different oxygen concentration in the magnetic field.

Right option is (b) It is a slow process

The BEST I can explain: During analysis of NO2 using Chemiluminescent analyser, NO2 is not made to REACT with ozone directly because it is a slow process. Hence, it is CONVERTED to NO using CATALYTIC reactions or converters.

Right answer is (b) By PLACING NO in a magnetic field

Easiest EXPLANATION: CO LASER emits RADIATION that can absorb NO. Absorption is enhanced by placing NO in a magnetic field.

Correct choice is (a) Carbon monoxide

Easy explanation: Polarographic CELLS are not SENSITIVE to carbon monoxide. They SHOW 0.1% error while measuring oxygen.

Right answer is (d) No INTERFERENCE from background gases

Explanation: SOLID state sensors are affected by interference from background gases. Some of them are HYDROGEN, isopropanol and ethyl and methyl mercaptan.

The correct CHOICE is (a) 2-10 HZ

Explanation: The chopping FREQUENCY used for industrial analysers in the simple infrared analyzer for gas ANALYSIS is 2-10 Hz. The chopper is motor driven.