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111.
Which of the following species is isoelectronic with $$CO?$$
A
$$HF$$
B
$${N_2}$$
C
$$N_2^ + $$
D
$$O_2^ - $$
Answer :
$${N_2}$$
Isoelectronic species means species having same number of electrons.
In $$CO;$$ no. of electrons = 6 + 8 = 14
In $${N_2};$$ no. of electrons =7 +7= 14
112.
The number of d-electrons retained in $$F{e^{2 + }}$$
( At no. of $$Fe = 26$$ ) ion is
A
4
B
5
C
6
D
3
Answer :
6
$$F{e^{ + + }}\left( {26 - 2 = 24} \right) = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^0}3{d^6}$$ hence no. of d electrons retained is 6.
[Two $$4s$$ electron are removed]
113.
The de Broglie wavelength of a tennis ball of mass 60$$g$$ moving with a velocity of 10 metres per second is approximately
Planck’s constant, $$h = 6.63 \times {10^{ - 34\,}}Js$$
116.
How many electrons are associated with the given set of quantum numbers, $$n = 3$$ and $$l = 1$$ ?
A
2
B
8
C
6
D
10
Answer :
6
$$n = 3,$$ $$l = 1$$ represents $$3p$$ orbital. Since $$p$$ has three orientations $${p_x},{p_y}$$ and $${p_z},6$$ electrons will show same quantum number values of $$n$$ and $$l.$$
117.
What is the maximum wavelength line in the Lyman series of $$H{e^ + }\,ion?$$
118.
The electronic configuration of an element is $$1{s^2},\,2{s^2}\,2{p^6},3{s^2}3{p^6}3{d^5},4{s^1}.$$ This represents its
A
excited state
B
ground state
C
cationic form
D
anionic form
Answer :
ground state
$$3{d^5}4{s^1}$$ system is more stable than $$3{d^4}4{s^2},$$ hence former is the ground state configuration.
119.
Which of the following statements do not form a part of Bohr’s model of hydrogen atom?
A
Energy of the electrons in the orbits are quantised
B
The electron in the orbit nearest the nucleus has the lowest energy
C
Electrons revolve in different orbits around the nucleus
D
The position and velocity of electrons in the orbit cannot be determined simultaneously
Answer :
The position and velocity of electrons in the orbit cannot be determined simultaneously
The main postulates of Bohr model of atom are
(i) The electrons in an atom revolve around the nucleus only in certain selected circular paths, called orbits.
(ii) The energy is emitted or absorbed only when the electrons jump from one energy level to another.
(iii) Only those orbits are permitted in which the angular momentum of the electron is a whole number multiple of $$\frac{h}{{2\pi }}$$ ( where, $$h$$ is Planck's constant ) that's why only certain fixed orbits are allowed, i.e. the momentum of an electron is quantised.
120.
What is the maximum number of emission lines when the excited electron of a hydrogen atom in $$n = 6$$ drops to ground state ?