491. $${{C_{60}}}$$, an allotrope of carbon cantains:

A $$12$$  hexagons and $$20$$  pentagons.
B $$18$$  hexagons and $$14$$  pentagons.
C $$16\,$$  hexagons and $$16\,$$  pentagons.
D $$20$$  hexagons and $$12$$  pentagons.
Answer :   $$20$$  hexagons and $$12$$  pentagons.
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492. Which of the following is the most basic oxide?

A $$A{l_2}{O_3}$$
B $$S{b_2}{O_3}$$
C $$B{i_2}{O_3}$$
D $$Se{O_2}$$
Answer :   $$B{i_2}{O_3}$$
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493. Which property of $$C{O_2}$$  makes it of biological and geochemical importance?

A Its acidic nature
B Its colourless and odourless nature
C Its low solubility in water
D Its high compressibility
Answer :   Its low solubility in water
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494. Which of the following statements is false?

A Radon is obtained from the decay of radium
B Helium is inert gas
C Xenon is the most reactive among the rare gases
D The most abundant rare gas found in the atmosphere is helium
Answer :   The most abundant rare gas found in the atmosphere is helium
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495. When $$Pb{O_2}\,$$ reacts with conc. $$HN{O_3}$$  the gas evolved is

A $$N{O_2}$$
B $${O_2}$$
C $${N_2}$$
D $${N_2}O$$
Answer :   $${O_2}$$
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496. A gas $$(X)$$  is obtained when copper reacts with dilute $$HN{O_3}.$$  The gas thus formed reacts with oxygen to give brown fumes of $$\left( Y \right).$$  $$\left( Y \right)$$  when dissolved in water gives an important acid $$(Z)$$  and the gas $$(X).$$  $$X, Y$$ and $$Z$$ respectively are

A $$NO;N{O_2};HN{O_3}$$
B $$N{O_2};NO;HN{O_3}$$
C $${N_2}O;NO;HN{O_2}$$
D $$NO;{N_2}O;HN{O_3}$$
Answer :   $$NO;N{O_2};HN{O_3}$$
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497. Which of the following statements is correct for $$CsB{r_3}$$ ?

A Itisa covalent compound.
B It contains $$C{s^{3 + }}$$ and $$B{r^ - }$$ ions.
C Itcontains $$C{s^ + }$$ and $$Br_3^ - $$ lons
D Itcontains $$C{s^ + }$$ and $$B{r^ - }$$ and lattice $$B{r_2}$$ molecule
Answer :   Itcontains $$C{s^ + }$$ and $$Br_3^ - $$ lons
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498. Regarding $${F^ - }$$  and $$C{l^ - }$$  which of the following statement $$(s)$$  is/are correct?
$$\left( {\text{i}} \right)C{l^ - }$$  can give up an electron more easily than $${F^ - }.$$
$$\left( {{\text{ii}}} \right)C{l^ - }$$  is a better reducing agent than $${F^ - }.$$
$$\left( {{\text{iii}}} \right)C{l^ - }$$  is smaller in size than $${F^ - }.$$
$$\left( {{\text{iv}}} \right){F^ - }$$  can be oxidised more readily than $$C{l^ - }.$$

A (i) and (ii)
B (i), (ii) and (iv)
C (iii) and (iv)
D Only (i)
Answer :   Only (i)
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499. Which one of the following is correct pair with respect to molecular formula of xenon compound and hybridization state of xenon in it ?

A $$Xe{F_4},s{p^3}$$
B $$Xe{F_2},sp$$
C $$Xe{F_2},s{p^3}d$$
D $$Xe{F_4},S{p^2}$$
Answer :   $$Xe{F_2},s{p^3}d$$
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500. Oleum is

A castor oil
B oil of vitriol
C fuming $${H_2}S{O_4}$$
D None of these
Answer :   fuming $${H_2}S{O_4}$$
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