When $MnO_2$ and $H_2SO_4$ are added to $NaCl$,the greenish-yellow gas liberated is:

The correct order of acidic strength is $.......?$

Which of the following properties of halogens increase with increasing atomic number?
$(I)$ Ionization energy $(II)$ Ionic radius
$(III)$ Bond energy of the $X_2$ molecule $(IV)$ Enthalpy of vaporisation

Atom $X$ belongs to group $17$ $(VIIA)$ and is not present in the second period. Choose the incorrect statement regarding $X$ $:-$

Assertion : The fluorine has lower reactivity.
Reason : $F-F$ bond has low bond dissociation energy.

Identify the group of the periodic table that contains the element $Astatine$ $(At)$.