Which one of the following is an example of a clean fuel ?
- A.Coke
- B.Propane
- C.Petrol
- D.Wax
Correct answer
Explanation
The correct answer is B, Propane. Propane is a light gaseous hydrocarbon that burns completely with a blue flame, leaving no smoke, soot or ash.
A clean fuel burns completely, gives high heat and releases few pollutants. Propane (C3H8), together with butane, makes up liquefied petroleum gas (LPG), the cooking gas used in Indian homes. Because it is a gas with small molecules, it mixes well with air and burns to carbon dioxide and water, with very little carbon monoxide or unburnt carbon. Compressed natural gas (CNG), which is mostly methane, is another clean fuel, used in buses and autorickshaws in Delhi to cut air pollution.
A is wrong because coke is a solid fuel that leaves ash and can give off carbon monoxide when air is limited.
C is wrong because petrol in engines releases carbon monoxide, unburnt hydrocarbons and nitrogen oxides.
D is wrong because wax, as in a candle, burns with a yellow, sooty flame, a sign of incomplete combustion.
Exam tip: LPG is mainly propane and butane; CNG is mainly methane; both are clean fuels.
Practice Questions
View allWhich one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
Read the full explanation →The frequency of ultrasound waves is
- A.less than 20 Hz
- B.between 20 Hz and 2 kHz
- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
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Ultrasound is sound with a frequency above 20,000 Hz, the upper limit of human hearing. Humans hear sound between about 20 Hz and 20 kHz.
Read the full explanation →A sample of 'soft soap' contains
- A.Caesium
- B.Potassium
- C.Calcium
- D.Magnesium
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Soft soaps are potassium salts of fatty acids, while ordinary hard bar soaps are sodium salts. Soap is made by saponification, heating an oil or fat with an alkali.
Read the full explanation →Which of the following sets of elements has the same valency?
- A.Na, Mg, Ca
- B.Na, Mg, Al
- C.Mg, Ca, K
- D.Mg, Ca, Ba
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Magnesium, calcium and barium are all alkaline earth metals of group 2, and each has a valency of 2. Elements in the same group of the periodic table have the same number of electrons in their outermost shell, and so the same valency.
Read the full explanation →Which one of the following is the correct order of the valencies of elements Ne, Si, N and Mg?
- A.Ne < Mg < N < Si
- B.Si < N < Mg < Ne
- C.Ne < N < Si < Mg
- D.Mg < Ne < N < Si
Show answer
Their valencies are neon 0, magnesium 2, nitrogen 3 and silicon 4. Valency is the combining capacity of an atom, the number of electrons it loses, gains or shares to reach a stable octet.
Read the full explanation →