Which one of the following is known as cetane?
- A.Hexadecane
- B.Heptadecane
- C.Octadecane
- D.Nonadecane
Correct answer
Explanation
The correct answer is A, Hexadecane. Cetane is the common name of n-hexadecane, C16H34, a straight-chain alkane with sixteen carbon atoms.
Cetane ignites very readily when compressed, which is exactly what a diesel engine needs, because diesel fuel is not lit by a spark but catches fire from the heat of compressed air. The cetane number of a fuel compares its ignition quality with this standard: pure cetane is given 100, and alpha-methylnaphthalene or a branched heptamethylnonane is used for the low end of the scale. A higher cetane number means a shorter delay between injection and ignition, a smoother and quieter engine and easier cold starts. It plays the role for diesel that the octane number plays for petrol.
Option B is wrong because heptadecane has seventeen carbons and is not called cetane. Option C is wrong because octadecane has eighteen carbons. Option D is wrong because nonadecane has nineteen carbons; none of these is the reference fuel.
Exam tip: Cetane (hexadecane, 100) rates diesel; iso-octane (100) and n-heptane (0) rate petrol.
Practice Questions
View allWhich one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
Show answer
Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
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Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
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Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →A lemon kept in water in a glass tumbler appears to be larger than its actual size. It is because of
- A.reflection of light
- B.scattering of light
- C.refraction of light
- D.polarization of light
Show answer
The lemon looks bigger because light from it bends as it passes from water through the curved glass into air.
Read the full explanation →Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?
- A.Most of the space in the atom is empty.
- B.The radius of the atom is about 10⁵ times the radius of the nucleus.
- C.Electrons move in a circular path of fixed energy called orbits.
- D.Nearly all the mass of the atom resides in the nucleus.
Show answer
. Orbits of fixed energy were proposed by Niels Bohr in 1913; Rutherford's experiment said nothing about the energy of electrons.
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