The tendency of BF₃, BCl₃ and BBr₃ to behave as Lewis acid decreases in the sequence:

BCl₃ > BF₃ > BBr₃
BBr₃ > BCl₃ > BF₃
BBr₃ > BF₃ > BCl₃
BF₃ > BCl₃ > BBr₃

Solution

p-p overlap between B and F is maximum due to identical size and energy of p-orbitals, so electron deficiency in boron of BF₃ is neutralized partially to the maximum extent by back donation. Hence BF₃ is least acidic.As the size of halogen atom increases from F to I, the extent of overlap between 2 p-orbital of B and a bigger p-orbital of halogen decreases. Therefore the electron deficiency of B increases.

According to the Bohr Theory, which of the following transitions in the hydrogen atom will give rise to the least energetic photon ?

n = 6 to n = 1
n = 5 to n = 4
n = 6 to n = 5
n = 5 to n = 3

Solution

Energy of photon obtained from the transition n = 6 to n = 5 will have least energy.

\(\Delta E = 13.6 Z^{2} \left ( \frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}} \right )\)

The ligand called π acid is:

CO
NH₃
\(C_{2}O_{4}^{2-}\)
Ethylenediamine

Solution

Due to back bonding present between metal and carbonyl ligand in metal carbonyl, CO is termed as π-acid ligand.

High basicity of Me₂NH relative to Me₃N is attributed to :

effect of solvent
inductive effect of Me
shape of Me₂NH
shape of Me₃N

Solution

Secondary amines are more basic than tertiary amines due to stabilisation of 2° amine by hydrogen bonding with solvent molecule.

A gas that cannot be collected over water is :

N²
O²
SO²
PH³

Solution

SO₂ is highly soluble in water and therefore cannot be collected over water.

Which of the following species has the highest dipole moment ?

NH₃
PH₃
AsH₃
SbH₃

Solution

Order of dipole moment

NH₃ > PH₃> AsH₃ > SbH₃

(Based upon electronegativity)

Which of the following is the correct decreasing order of acidic strength of

(i)Methanoic acid (ii)Ethanoic acid
(iii)Propanoic acid (iv)Butanoic acid

(i) > (ii) > (iii) > (iv)
(ii) > (iii) > (iv) > (i)
(i) > (iv) > (iii)> (ii)
(iv) > (i) > (iii)> (ii)

Solution

An electron releasing substituent (+I) intensify the negative charge on the anion resulting in the decrease of stability and thus decreases the acidity of the acid. Hence acid character decreases as the +I-effect of the alkyl group increases as
\(CH_{3}^{-}<CH_{3}CH_{2}^{-}<CH_{3}CH_{2}CH_{2}^{-}<CH_{3}CH_{2}CH_{2}CH_{2}^{-}\)
Hence the order becomes :(i) > (ii) > (iii) > (iv)

Solution

The reaction of toluene with Cl₂ in presence of FeCl₃ gives ‘X’and reaction in presence of light gives ‘Y’. Thus, ‘X’and ‘Y’ are :

X= Benzal chloride, Y = o – Chlorotoluene
X = m– Chlorotoluene, Y = p –Chlorotoluene
X = o –and p – Chlorotoluene,Y = Trichloromethylbenzene
X= Benzyl chloride, Y = m– Chlorotoluene

Solution

Solution

By 2× (ii) – (i) + (iii) H₂(g) + 2C(s) ⟶ C₂H₂(g), ?G° = 209 kJ

B.O.D. test or biochemical oxygen demand test is made for measuring

air pollution
water pollution
noise pollution
soil pollution

Solution

Strength of sewage or degree of water pollution is measured in terms of BOD (Biochemical oxygen demand) value.

In Kjeldahl’s method for the estimation of nitrogen, the foumula used is

%N = \(\frac{1.4VW}{N}\)
%N = \(\frac{1.4VW}{V}\)
%N = \(\frac{VNW}{1.8}\)
%N = \(\frac{1.4VN}{W}\)

Which of the following is not correct for electronic distribution in the ground state ?

Solution

According to Hund’s rule electron pairing in P, d and f orbitals cannot occur until each orbital of a given subshell contains one electron each or is singly occupied.

Cyclohexanol (I), acetic acid(II), 2, 4, 6-trinitrophenol (III)and phenol(IV) are given. In these the order of decreasing acidic character will be :

III > II > IV > I
II > III > I > IV
II > III > IV > I
III > IV > II > I

Solution

Which of the following does not show optical isomerism?

(en = ethylenediamine)

[Co(NH³)³Cl³]⁰
[Co(en)Cl²(NH³)²]⁺
[Co(en)³]³⁺
[Co(en)²Cl²]⁺

Solution

The octahedral coordination compounds of the type MA³B³ exhibit fac-mer isomerism.

The vapour pressure of two liquids‘P’ and‘Q’ are 80 and 60 torr, respectively. The total vapour pressure of solution obtained by mixing 3 mole of P and 2 mole of Q would be

72 torr
140 torr
68 torr
20 torr

Solution

For azimuthal quantum number l = 3, the maximum number of electrons will be

2
6
Zero
14

Solution

l = 3 means f-subshell. Maximum no. of electrons = 4l + 2 = 4 × 3 + 2 = 14

In an irreversible process taking place at constant T and P and in which only pressure-volume work is being done, the change in Gibbs free energy (dG) and change in entropy (dS), satisfy the criteria

(dS)_{V, E} > 0, (dG)_{T, P} < 0
(dS)_{V, E} = 0, (dG)_{T, P} = 0
(dS)_{V, E} = 0, (dG)_{T, P} > 0
(dS)_{V, E} < 0, (dG)_{T, P} < 0

Solution

For spontaneous reaction, dS > 0 and dG should be negative i.e., < 0.

Solution

The rate constant is doubled when temperature increases from 27°C to 37°C. Activation energy in kJ is

Solution

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