The anti-knocking agent of unleaded petrol is
(a) Dibromoethane
(b) Methyl ethyl ether
(c) Propane Tetraethyl lead
(d) Methyl Tertiary Butyl Ether

Hint: The anti knocking agent which is present in unleaded petrol is an organic compound that is a volatile, flammable, and colorless liquid that is sparingly soluble in water. It’s molar mass is ${ 8 }{ 8 }{ \cdot }{ 15 }{ g }/{ mol }$.

Complete step by step answer:
The anti knocking agent of unleaded petrol is Methyl Tertiary Butyl Ether(MTBE) . It is also known as tert - butyl methyl ether. It is an organic compound with structural formula $\left( { CH }_{ 3 } \right) _{ 3 }{ COC }{ H }_{ 3 }$ . Methyl tert-butyl ether is a flammable liquid that has been used as an additive for unleaded gasoline since the 1980s. MTBE increases octane and oxygen levels in gasoline and reduces pollution emissions which in turn helps in protecting the environment from pollution and harmful gases.

Additional Information: MTBE is unstable toward reaction with strong acids and it also reacts dangerously with bromine.
MTBE is also used as a solvent. It is also used for medical purposes. For example, it is used to treat gallstones. MTBE is injected directly into the gallbladder to dissolve gallstones from that site or area.
Nowadays, alternatives of MTBE are also available including ethanol and other ethers such as ETBE. Ethanol is said to be safe by agricultural and other interest groups. An alternative used for ethanol is Ethyl tert-butyl ether (ETBE), which is manufactured from ethanol and isobutene. Its performance as an additive is analogous to MTBE.
So, the correct answer is ‘Methyl Tertiary Butyl Ether'.

Note: Though MTBE is very useful but in many places or countries it is banned now as if human engulfed due to some reason high doses of it, skin and eye irritation is seen in them. MTBE is usually found in some water sources, due to leaking underground gasoline storage tanks. Even at very low concentrations, MTBE gives water an unpleasant taste.