(a) The main advantages are:
(i) It is made from renewable energy sources i.e., sugarcane and com which are grown in the field.
(ii) It has higher octane rating.
(iii) Due to the presence of oxygen in ethanol, poisonous gases like CO and unburnt hydrocarbon are emitted to a lesser extent.
(iv) Less dependence on imported oils thereby promoting the economy of our country.
(b) The main disadvantages are :
(i) It has one-third the energy content than the gasoline. Thus drivers will need more ethanol than gasoline to drive the same distance.
(ii) Ethanol can absorb water and dust more easily and hence corrodes engine made up of Al.
(iii) It produces cancer causing emissions such as acetaldehyde and formaldehyde forty times more than gasoline. Social awareness, Social awareness, eco-friendiness are the values associated with the use of ethanol as fuel.

(i) \({ CH }_{ 3 }-{ CH }_{ 2 }-CH={ CH }_{ 2 }+{ H }_{ 2 }O\overset { { H }^{ + } }{ \longrightarrow } { CH }_{ 3 }{ CH }_{ 2 }(OH){ CH }_{ 3 }\)
Since X forms bisulphate and 2, 4-dinitrophenylhydrazone, it means Xhas carbonyl group formed due to oxidation of alcohol. This oxidation is due to coating of metal (Cu).
 \({ CH }_{ 3 }{ CH }_{ 2 }(OH){ CH }_{ 3 }\longrightarrow { CH }_{ 3 }{ CH }_{ 2 }CO{ CH }_{ 3 }(ketone/X)+{ H }_{ 2 }I\)
(ii) Alcohol and X both give iodoform test. 
(iii) Alcohol and X can be separated by
(a) Distillation
(b) BisulpIilte formation only (X) forms Bisulphite complex (s) which can be decomposed.
(iv) Usha lacks critical awareness of chemistry.

(i) Methyl alcohol is easily oxidized to formaldehyde and then to formic acid which may cause blindness and death. 
(ii) Doctors give an intra venous infusion of diluted ethanol the enzyme responsible for oxidation of HCHO to acid is swamped allowing time for kidneys to excrete methanol. 
(iii) People should be educated not to drink cheap alcohol from unauthorized sources. It is not worth saving money when the life get endangered. If at all one has to drink, the stuff must be purchased from an authorized source.

(i) Teacher preferred denatured alcohol over absolute alcohol as it would be unfit for drinking. As commercial alcohol is mixed with copper sulphate to give it a colour and pyridine to give a foul smell, which makes absolute alcohol unfit for drinking and called as denatured alcohol. 
(ii) As the teacher was ordering ethanol for school laboratory, maintaining discipline, repsonsible behaviour and social obligation were values kept in her mind, while taking decision.