4. Metallic oxide turn litmus to .

Explanation:

Metal oxides are generally basic in nature.

When metal oxides react with acid they form respective metal salt and water.

Acid + Metal Oxide => Salt + Water

Neutralization Reaction :

Acid + Base => Salt + Water

This is similar to neutralization reaction where base comes instead of Metal oxide. Hence it can be concluded that Metal oxide is a base.

So Bases turn Red litmus to blue.

Hence the solution of any metal oxide will turn Red litmus to Blue but it has no effect on the Blue Litmus paper.

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.