Chemistry

NEET Class 12

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1.

Assertion : The quantized energy of an electron is largely determined by its principal quantum number.

Reason : The principal quantum number n is a measure of the most probable distance of finding the electron around the nucleus.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

A.

If both assertion and reason are true and reason is the correct explanation of assertion.

$\mathrm{E}=-\frac{2{\mathrm{\pi}}^{2}{\mathrm{k}}^{2}{\mathrm{m}}_{\mathrm{e}}^{4}}{{\mathrm{n}}^{\mathrm{h}}{\mathrm{h}}^{2}}$

where n = principal quantum number which has only integral value, it follows that total energy is quantized.

2.

Assertion : Copper metal gets readily corroded in acidic aqueous solution.

Reason : Free energy change for this process is negative.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

D.

If both assertion and reason are false.

Non-oxidising acids (HCl and dil.H_{2}SO_{4}) do not have any effect on copper. However they dissolve the metal in presence of air. As it is a nonspontaneous process so, $\u2206$G can not be -ve.

3.

Assertion : Many endothermic reactions that are not spontaneous at room temperature become spontaneous at high temperature.

Reason : Entropy of the system increases with increase in temperature.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

B.

If both assertion and reason are true but reason is not the correct explanation of assertion.

The factor T$\u2206$S increases with increase in temperature.

4.

Assertion : According to Le-Chatelier's principle addition of heat to an equilibrium solid $\rightleftharpoons $liquid results in decrease in the amount of solid.

Reason : Reaction is endothermic, so on heating forward reaction is favoured.

If both assertion and reason are true and reason is the correct explanation of assertion

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

A.

If both assertion and reason are true and reason is the correct explanation of assertion

Solid+ heat $\rightleftharpoons $liquid. So on heating forward reaction is favoured and amount of solid will decrease.

5.

A unit cell of sodium chloride has four formula units. The edge length of the unit cell is 0.564 nm. What is the density of sodium chloride?

1.2 g/cm

^{3}2.165g/cm

^{3}3.64 g/cm

^{3}4.56 g/cm

^{3}

B.

2.165g/cm^{3}

$\mathrm{Density}=\frac{\mathrm{nM}}{{\mathrm{N}}_{\mathrm{a}}\times {\mathrm{a}}^{3}}\phantom{\rule{0ex}{0ex}}=\frac{4\times 58.3}{6.023\times {10}^{23}\times {\left(5.64\times {10}^{-8}\right)}^{3}}=2.17\mathrm{g}/{\mathrm{cm}}^{3}$

6.

The correct order of increasing [H_{3}O+] in the following aqueous solutions is

0.01 M H

_{2}S < 0.01 M H_{2}SO_{4}< 0.01M NaCl< 0.01 M NaNO_{2}0.01 M NaCl<0.01 M NaNO

_{2}<0.01 M H_{2}S <0.01 M H_{2}SO_{4}0.01 M NaNO

_{2 }< 0.01 M NaCl < 0.01 M H_{2}S <0.01 M H_{2}SO_{4}0.01 M H

_{2}S < 0.01 M NaNO_{2}< 0.01 M NaCl <0.01M H_{2}SO_{4}

C.

0.01 M NaNO_{2 }< 0.01 M NaCl < 0.01 M H_{2}S <0.01 M H_{2}SO_{4}

H_{2}SO_{4} is strong acid having pH< 7. NaNO_{2} on hydrolysis gives alkaline solution of pH > 7.NaCl is neutral and H_{2}S is weak acid.

7.

Assertion : If H_{2} and Cl_{2} enclosed separately in the same vessel exert pressure of 100 and 200 mm respectively, their mixture in the same vessel at the same temperature will exert a pressure of 300 mm.

Reason : Dalton's law of partial pressures states that total pressure is the sum of partial pressures.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

D.

If both assertion and reason are false.

H_{2 }and Cl_{2 }react chemically. Hence Dalton's law is not applicable. Dalton's law states that "at a given temperature, the total pressure exerted by two or more non-reacting gases occupying a definite volume is equal to the sum of the partial pressures of the component gases."

8.

The dissociation equilibrium of a gas AB_{2} can be represented as

$2{\mathrm{AB}}_{{2}_{\left(\mathrm{g}\right)}}\leftrightharpoons 2{\mathrm{AB}}_{\left(\mathrm{g}\right)}+{\mathrm{B}}_{{2}_{\left(\mathrm{g}\right)}}$

The degree of dissociation is x and is small compared to 1. The expression relating the degree of dissociation (x) with equilibrium constant K_{P} and total pressure p is

(2K

_{p}/p)^{1/2}K

_{p}/p2K

_{p}/p(2kp/p)

^{1/3}

D.

(2kp/p)^{1/3}

$2{\mathrm{AB}}_{2\left(\mathrm{g}\right)}\rightleftharpoons 2{\mathrm{AB}}_{\left(\mathrm{g}\right)}+{\mathrm{B}}_{2\left(\mathrm{g}\right)}$

Initial 2 0 0

Equilibrium 2(1-x) 2x x

Moles at equilibrium = 2(1-x)+2x+x =2-2x +2x+x

= x+2

${\mathrm{K}}_{\mathrm{p}}=\frac{\left[{\mathrm{P}}_{\mathrm{AB}}{]}^{2}\right[{\mathrm{P}}_{{\mathrm{B}}_{2}}]}{\left[{\mathrm{P}}_{{\mathrm{AB}}_{2}}\right]}=\frac{{\left[{\displaystyle \frac{2\mathrm{x}}{\mathrm{x}+2}}\times \mathrm{p}\right]}^{2}\left[{\displaystyle \frac{\mathrm{x}}{2+\mathrm{x}}}\times \mathrm{p}\right]}{{\left[{\displaystyle \frac{2(1-\mathrm{x})}{\mathrm{x}+2}}\times \mathrm{p}\right]}^{2}}\phantom{\rule{0ex}{0ex}}=\frac{{\displaystyle \frac{4{\mathrm{x}}^{2}}{\mathrm{x}+2}}\times \mathrm{p}}{4(1-\mathrm{x}{)}^{2}}=\frac{4{\mathrm{x}}^{2}\times \mathrm{p}}{2}\times \frac{1}{4}$

$\mathrm{x}={\left(\frac{2\mathrm{Kp}}{\mathrm{p}}\right)}^{1/3}(\mathrm{as}1-\mathrm{x}\approx 1,2+\mathrm{x}\approx 2)$

9.

Percentage of Se (at. mass= 78.4) in peroxidase anhydrase enzyme is 0.5% by weight, then minimum molecular mass ofperoxidase anhydrase enzyme is

1.576 x 10

^{4}1.576 X 10

^{3}15.76

2.136 X 10

^{4}.

A.

1.576 x 10^{4}

The enzyme must contains at least one atom of Se.

0.5 g of Se is present in 100gm of enzyme

78.4 g of Se will be present in =$\frac{100\times 78.4}{0.5}=1.576\times {10}^{4}\mathrm{g}\mathrm{of}\mathrm{enzymes}.$

10.

The correct order of dipole moment is

CH

_{4}<NF_{3 }<NH_{3 }<H_{2}ONF

_{3}<CH_{4}<NH_{3}<H_{2}ONH

_{3}<NF_{3}<CH_{4}<H_{2}OH

_{2}O <NH_{3}<NF_{3 }<CH_{4}

A.

CH_{4} <NF_{3 }<NH_{3 }<H_{2}O

In H_{2}O electronegativity difference is highest. So, dipole moment is highest in this. CH_{4} is a symmetrical tetrahedral structure and its dipole moment is zero.

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