NEET 2017 Chemistry Question Paper with Answer and Solution

(D) The letter '$D$' in $D$-glucose refers to the configuration of the hydroxyl $(-OH)$ group attached to the penultimate chiral carbon (the chiral carbon furthest from the carbonyl group). If the $-OH$ group is on the right side in the Fischer projection,it is designated as '$D$'.

(C) In the froth flotation process,$NaCN$ is used as a depressant to separate $ZnS$ from $PbS$.
$NaCN$ selectively prevents $ZnS$ from forming froth by forming a soluble complex $Na_2[Zn(CN)_4]$,while $PbS$ forms froth and is collected.

(A) In Group $13$ elements,the stability of the $+1$ oxidation state increases down the group due to the inert pair effect.
As we move from $B$ to $Tl$,the $ns^2$ electrons become more reluctant to participate in bonding.
Therefore,the stability of the $+1$ oxidation state follows the order: $B < Al < Ga < In < Tl$.

$(C)$ In reaction $(A)$, the carbonyl group of cyclopentanone undergoes nucleophilic addition with $2,4-$dinitrophenylhydrazine, which is a characteristic reaction of aldehydes and ketones. Thus, $(A)$ matches with $(R)$.
In reaction $(B)$, the tertiary alcohol undergoes acid-catalyzed dehydration to form a carbocation, which then undergoes intramolecular electrophilic aromatic substitution (Friedel-Crafts alkylation) to form the bicyclic product. Thus, $(B)$ matches with $(P)$.
In reaction $(C)$, the thiol group acts as a nucleophile after deprotonation by the base, and it attacks the carbon atom bearing the chlorine atom, leading to an intramolecular nucleophilic substitution reaction. Thus, $(C)$ matches with $(Q)$.
Therefore, the correct match is $A-R, B-P, C-Q$.

(A) The rate of $S_N 1$ reaction depends on the stability of the carbocation intermediate formed after the departure of the leaving group.
In $H_2C=CH-CH_2Cl$,the carbocation formed is $H_2C=CH-CH_2^+$,which is resonance-stabilized by the adjacent double bond.
Chlorobenzene and $CH_2=CHCl$ are vinylic/aryl halides where the $C-Cl$ bond has partial double bond character,making them very unreactive towards $S_N 1$.
$CH_3CH_2Cl$ forms a primary carbocation,which is less stable than the resonance-stabilized allylic carbocation.
Therefore,$H_2C=CH-CH_2Cl$ reacts fastest.

(D) An amino acid is optically active if it contains a chiral carbon atom (an asymmetric carbon bonded to four different groups).
In glycine $(NH_2-CH_2-COOH)$,the central carbon atom is bonded to two hydrogen atoms.
Since two groups attached to the central carbon are identical,it is achiral and therefore not optically active.

(B) The cell reaction is the sum of the cathode and anode reactions:
Cathode: $Ag_2O + H_2O + 2e^- \rightarrow 2Ag + 2OH^- ; E^{\circ} = 0.344 \, V$
Anode: $Zn \rightarrow Zn^{2+} + 2e^- ; E^{\circ} = +0.760 \, V$
Overall $E_{cell}^{\circ} = E_{cathode}^{\circ} - E_{anode}^{\circ} = 0.344 - (-0.760) = 1.104 \, V$
Using the formula $\Delta G^{\circ} = -nFE_{cell}^{\circ}$ where $n = 2$:
$\Delta G^{\circ} = -2 \times 96,500 \times 1.104 \, J \, mol^{-1} = -213,072 \, J \, mol^{-1}$
Converting to $kJ \, mol^{-1}$: $\Delta G^{\circ} = -213.072 \, kJ \, mol^{-1}$