Question

what would be the colour of litmus paper in a solution of sodium carbonate

Answer 1

Hope this will help u :-
the color of the litmus paper will turn into blue color because sodium carbonate is basic in nature

Answer 2

The colour of litmus paper in a solution of sodium carbonate is 'blue'.

Sodium carbonate is a salt with chemical formula $\mathrm{Na}_{2} \mathrm{CO}_{3}$. It is formed by the reaction of NaOH with $\mathrm{H}_{2} \mathrm{CO}_{3}$. Here NaOH is a strong base and $\mathrm{H}_{2} \mathrm{CO}_{3}$ is a weak acid. Hence the salt formed will be a basic salt.  

With a basic salt, the red litmus changes to blue color. Therefore we can say that the nature of salt always depends on the acid and base it formed during the reaction.