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1

AIPMT 2014

MCQ (Single Correct Answer)
In the Kjeldahl's method for estimation of nitrogen present in a soil sample, ammonia evolved from 0.75 g of sample neutralized 10 mL of 1 M H2SO4. The percentage of nitrogen in the soil is
A
37.33
B
45.33
C
35.33
D
43.33

Explanation

10 ml, 1 M H2SO4 = 20 ml, 1 M NH3

$$ \because $$ wt of N in one mole NH3 = 14

$$ \therefore $$ 20 × 10–3 mol NH3 $$ \to $$ 20 × 10–3 × 14 nitrogen

$$ \therefore $$ 0.75 g of sample contains = $${{14 \times 20 \times {{10}^{ - 3}}} \over {0.75}} \times 100$$

= 37.33%
2

NEET 2013 (Karnataka)

MCQ (Single Correct Answer)
Homolytic fission of the following alkanes forms free radicals CH3 $$-$$ CH3, CH3 $$-$$ CH2 $$-$$ CH3, (CH3)2CH $$-$$ CH3, CH3 $$-$$ CH2 $$-$$CH(CH3)2.
Increasing order of stability of the radicals is
A
$$\eqalign{ & {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet \, - \,C{H_2}C{H_3}\, < C{H_3}\, - \,\mathop C\limits^ \bullet H - \,C{H_3} \cr & < C{H_3}\, - \,\mathop C\limits^ \bullet {H_2}\, < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet \cr} $$
B
$$\eqalign{ & C{H_3}\, - \,\mathop C\limits^ \bullet {H_2}\, < \,C{H_3}\, - \,\mathop C\limits^ \bullet HH\, - \,C{H_3}\, < \cr & {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet \, - \,C{H_2}\, - \,C{H_3}\, < \,{\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet \cr} $$
C
$$\eqalign{ & C{H_3} - \mathop C\limits^ \bullet {H_2} < C{H_3} - \mathop C\limits^ \bullet H - C{H_3} < \cr & {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet \, < {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet \, - C{H_2}C{H_3} \cr} $$
D
$$\eqalign{ & {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet \, < {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet \, - C{H_2}C{H_3} < \cr & C{H_3} - \mathop C\limits^ \bullet H - C{H_3} < C{H_3} - \mathop C\limits^ \bullet {H_2} \cr} $$

Explanation

Stability depends on number of hyperconjugative structure. More the number of hyperconjugative structure, the greater is the stability.
3

NEET 2013 (Karnataka)

MCQ (Single Correct Answer)
Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour formed corresponds to which of the following formulae?
A
Fe3[Fe(CN)6]2
B
Fe4[Fe(CN)6]3
C
Fe4[Fe(CN)6]2
D
Fe3[Fe(CN)6]3

Explanation

The prussian blue colour is of Fe4 [Fe(CN)6]3 ferric ferrocyanide.
4

NEET 2013 (Karnataka)

MCQ (Single Correct Answer)
What is the hybridisation state of benzyl carbonium ion?

A
sp2
B
spd2
C
sp2d
D
sp3

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