The incorrect statement among the following regarding helium is -

1. It is used to produce and sustain powerful superconducting magnets.

2. It is used as a cryogenic agent for carrying out experiments at low temperatures.

3. It is used in filling balloons for meteorological observations because it is lighter and non-inflammable.

4. It is used as a dilute for oxygen in modern diving apparatus because of its high solubility in blood.

Assertion : $Pb{I}_4$  is not known probably because of the oxidising power of Pb(IV) and reducing power of $I^{-}$.

Reason :  Iodide stabilizes higher oxidation state.

Assertion : $P_4{O}_{10}$ is not used to dry $N{H}_3$.

Reason : $P_4{O}_{10}$ is acidic and $N{H}_3$ is basic.

Assertion : $HN{O}_3$  is stronger acid than $HN{O}_2$.

Reason : In $HN{O}_3$ there are two nitrogen to oxygen bonds where as in $HN{O}_2$ there is only one.

Assertion : $HN{O}_3$ oxides sulphur to $H_{2}S{O}_4$  acid ( S + VI) but only oxidizes selenium to $H_{2}Se{O}_3$ ( Se + IV ).

Reason : In Selenium atoms, the electrons are more tightly held by the nucleus on account of increased nuclear charge.

Assertion : Sulphur dioxide is more powerful reducing agent in alkaline medium than in acidic
medium.

Reason :  Sulphur dioxide reacts with hydrogen sulphide in presence of moisture and sulphur is
precipitated.

Assertion : $S{F}_6$ is used as a gaseous insulator in high voltage generators.

Reason :  It is inert and has good dielectric properties.

Assertion : Finely divided iron does not form ferric chloride with hydrochloric acid.

Reason :  Hydrochloric acid produces hydrogen gas with iron.

Assertion : $Xe{F}_6$ reacts with small quantity of water to form $XeO{F}_4$.

Reason : $Xe{F}_6$ reacts with glass and form $XeO{F}_4$.

Which one of the following does not exist?

1. XeOF₄

2. NeF₂

3. XeF₂

4. XeF₆