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1

NEET 2013

MCQ (Single Correct Answer)
Which of the following is electron-deficient ?
A
(BH3)2
B
PH3
C
(CH3)2
D
(SiH3)2

Explanation

Boron hydrides are electron deficient compound because boron atom has three half-filled orbitals in excited state.
2

AIPMT 2012 Mains

MCQ (Single Correct Answer)
During change of O2 to O$$_2^{ - }$$ ion, the electron adds on which one of the following orbitals ?
A
$${\pi ^ * }$$ orbital
B
$$\pi $$ orbital
C
$${\sigma ^ * }$$ orbital
D
$$\sigma $$ orbital

Explanation

Electronic configuration of O2

$$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2{\pi ^*}2p_x^1{\pi ^*}2p_y^1$$

Thus the incoming electron will enter in $$\pi ^*2p_x$$ to form $$O_2^+$$
3

AIPMT 2012 Mains

MCQ (Single Correct Answer)
Four diatomic species are listed below. Identify the correct order in which the bond order is increasing in them
A
$$NO < {O_2}^ - < {C_2}^{2 - } < He_2^ + $$
B
$${O_2}^ - < NO < {C_2}^{2 - } < He_2^ + $$
C
$${C_2}^{2 - } < He_2^ + < {O_2}^ - < NO$$
D
$$He_2^ + < {O_2}^ - < NO < {C_2}^{2 - }$$

Explanation

Diatomic species Bond order
NO 2.5
$$O_2^-$$ 1.5
$$C_2^{2-}$$ 3.0
$$He_2^+$$ 0.5
The increasing order: $$He_2^ + < {O_2}^ - < NO < {C_2}^{2 - }$$
4

AIPMT 2012 Prelims

MCQ (Single Correct Answer)
The pair of species with the same bond order is
A
O$$_2^{2 - }$$, B2
B
O$$_2^{ + }$$, NO+
C
NO, CO
D
N2, O2

Explanation

O2- $$ \to $$ 1

B2 $$ \to $$ 1

O2+ $$ \to $$ 2.5

NO+ $$ \to $$ 3

NO $$ \to $$ 2.5

CO $$ \to $$ 3

N2 $$ \to $$ 3

O2 $$ \to $$ 2

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