Correct Answer:
e) Hot water in a thermos flask
Explanation:
Hot water in a thermos flask is an example for an isolated system where neither energy nor matter
can enter or exit. Boiling a soup in an open sauce pan in a stove is an example for open system in
which, it can freely exchange its energy and matter with its surroundings. Cooking rice in a pressure
cooker is an example for a closed system where it can exchange only energy with its surroundings. A
pot of boiling water and an open tank of water is an example for an open system as the matter gets
exchanged with its surroundings.
Question 4
The bond order for helium molecule is
a) 1
b) 2
c) 2.5
d) 3
e) 0
Correct Answer:
e) 0
Explanation:
The
electronic configuration of helium in the ground state is represented as (σ
1s
)
2
and in the excited
state, it is represented as (σ
*
1s
)
2
.
So, number of electrons in bonding molecular orbital (N
b
) is 2 and number of electrons in antibonding
molecular orbital (N
a
) is 2.
The bond order for He
2
is 0, so the molecule does not exist.
Question 5
The order of ionisation energy is
a) s< p < d < f
b) s> p > d > f
c) s> p > d < f
d) s< d < p < f
e) s< p < f < d
Correct Answer:
b) s > p > d > f
Explanation:
The ionisation energy depends upon the atomic radius. As the s-orbital electrons remain closer to the
nucleus, the ionisation energy will be greater for s- orbital than for p-, d- and f- orbitals.
