NEET Practice Questions (MCQs) with Answers & Solutions

2-chloropropane has $\beta$-hydrogens on both adjacent methyl groups. Heating with alcoholic KOH will cause an elimination reaction (dehydrohalogenation), removing a chlorine atom and a hydrogen atom from an adjacent carbon, resulting in the formation of propene.

While both aqueous and alcoholic KOH can act as a base/nucleophile, alcoholic KOH is a stronger base and a weaker nucleophile due to the steric hindrance of the alkoxide ion formed in alcohol, favoring elimination (E2) over substitution (SN2). Aqueous KOH, being a strong nucleophile, would primarily lead to nucleophilic substitution (formation of alcohol).

In an elimination reaction, the $\alpha$-carbon (bearing the halogen) and the $\beta$-carbon (losing a hydrogen) both change their hybridization state. The $\alpha$-carbon, initially sp3 hybridized, becomes part of a carbon-carbon double bond, thus transitioning to sp2 hybridization.

The NCERT text explicitly states, 'When a haloalkane with $\beta$-hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from $\beta$-carbon and a halogen atom from the $\alpha$-carbon atom.' This confirms the necessity of a $\beta$-hydrogen. They typically form alkenes, can be unimolecular (E1) or bimolecular (E2), and are favored by higher temperatures and strong bases.

According to Table 15.1 and the accompanying text, 'Persons with 'AB' group can accept blood from persons with AB as well as the other groups of blood. Therefore, such persons are called 'universal recipients'.' This is because their plasma contains no anti-A or anti-B antibodies, allowing them to receive blood from all ABO groups without agglutination.

The context states: 'A special case of Rh incompatibility (mismatching) has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus.' This condition results when the mother's immune system, exposed to the Rh antigen from the foetus, produces antibodies that can then attack a subsequent Rh+ve foetus.

The NCERT text explains: 'Rh antigens of the foetus do not get exposed to the Rh-ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta.' This prevents the mother from forming antibodies during the first pregnancy.

Table 15.1 shows that for blood group O, the 'Antigens on RBCs' column lists 'nil', meaning both A and B antigens are absent. This is why group O individuals are 'universal donors'.

The text states: 'An Rh-ve person, if exposed to Rh+ve blood, will form specific antibodies against the Rh antigens.' This indicates a delayed immune response where antibodies are produced upon initial exposure, rather than an immediate reaction.

The context explicitly states: 'You probably know that during blood transfusion, any blood cannot be used; the blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping (destruction of RBC).'