Which one of the following statements regarding helium is incorrect ?

It is used to produce and sustain powerful superconducting magnets.
It is used as a cryogenic agent for carrying out experiments at low temperatures.
It is used to fill gas balloons instead of hydrogen because it is lighter and non-inflammable.
It is used in gas-cooled nuclear reactors.

Solution

Helium is twice as heavy as hydrogen it is in flammable but not lighter than hydrogen. Helium has the lowest melting and boiling point of any element which makes liquid helium an ideal coolant for many extremely low temperature application such as super conducting magnet and cryogenic research where temperature close to absolute zero are needed. He is used in gas cool edatomic reactors as a heat transfer agent.

Perdisulphuric acid has the following bond

In nitrogen family, the H-M-H bond angle in the hydrides gradually becomes closer to 90º on going from N to Sb. This shows that gradually

Solution

With the decrease in the electronegativity of central atom the bond angle decreases

PbO₂ on reaction with conc. HNO₃ gives

Solution

PbO₂ is a strong oxidising agent. It reacts with conc.HNO₃ as shown:

\(pbO_{2}+2HNO_{3}\rightarrow pb(NO_{3})_{2}+H_{O}+\frac{1}{2}O_{2}\)

Noble gases are group of elements which exhibit

Which one of the following noble gases is not found in the atmosphere

Solution

Rn because it is radioactive element obtained by the disintegration of radium

\(_{88}Ra^{226}\rightarrow _{86}Rn^{222}+_{2}He^{4}\)

Hydrolysis of NCl³ gives NH³ and X. Which of the following is X ?

Solution

Completing the reaction, we get

\(NCL_{3}+3H_{2}O\rightarrow \underset{'X'}{3HCIO}+NH_{3}\)

Noble gases do not react with other elements because

For advertisement, the coloured discharge tubes contain :

End-product of the hydrolysis of XeF₆ is

Solution

XeF₆+ 3H₂O → XeO₃ + 6HF

∴Complete hydrolys is of XeF₆ gives XeO₃(an explosive).

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