641. The variation of the boiling point of the hydrogen halides is in the order $$HF > HI > HBr > HCl.$$      What explains the higher boiling point of hydrogen fluoride?

A The electronegativity of fluorine is much higher than for other elements in the group
B There is strong hydrogen bonding between $$HF$$  molecules
C The bond energy of $$HF$$  molecules is greater than in other hydrogen halides
D The effect of nuclear shielding is much reduced in fluorine which polarises the $$HF$$  molecule
Answer :   There is strong hydrogen bonding between $$HF$$  molecules
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642. The reddish brown coloured gas formed when nitric oxide is oxidised by air is

A $${N_2}{O_5}$$
B $${N_2}{O_4}$$
C $$N{O_2}$$
D $${N_2}{O_3}$$
Answer :   $$N{O_2}$$
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643. Match the uses of the metal aluminium given in column I with its properties given in column II and mark the appropriate choice.
Column I Column II
a. Transmission cables 1. High malleability
b. Aircraft body 2. High electrical conductivity
c. Packing industry 3. High thermal conductivity
d. Utensile 4. Light and tough alloys

A a - 2, b - 1, c - 3, d - 4
B a - 4, b - 3, c - 2, d - 1
C a - 2, b - 4, c - 1, d - 3
D a - 3, b - 4, c - 1, d - 2
Answer :   a - 2, b - 4, c - 1, d - 3
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644. Which one of the following properties is not shown by NO?

A It is diamagnetic in gaseous state
B It is neutral oxide
C It combines with oxygen to form nitrogen dioxide
D It’s bond order is 2.5
Answer :   It is diamagnetic in gaseous state
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