Answer: Option (a) is the correct answer.
Explanation:
Strontium chloride ([tex]SrCl_{2}[/tex]) is an ionic compound. And, as it is ionic in nature so there will be strong force of attraction between the two oppositely charged ions that is, [tex]Sr^{2+}[/tex] and [tex]Cl^{-}[/tex].
At room temperature, [tex]SrCl_{2}[/tex] exists in solid state.
Whereas ethane ([tex]C_{2}H_{6}[/tex]) at room temperature exists as a gas.
Chemical formula of water is [tex]H_{2}O[/tex] and at room temperature it exists in liquid state.
[tex]Cl_{2}[/tex] is a dichlorine molecule and it exists as a gas at room temperature.
Thus, we can conclude that out of the given options [tex]SrCl_{2}[/tex] would you expect to be the hardest at room temperature.
