What will be the action of the following substances on litmus paper?​

Dry $\text{HCl}$ gas, Moistened ${\text{NH}}_3$ gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.

Lemon juice, carbonated soft drink and curd contain acids. Therefore, they turn litmus paper into red. ​

​Moistened ${\text{NH}}_3$ is a base while soap solution contains base. Therefore, they turn litmus blue.​

Dry $\text{HCl}$ has no effect on litmus as it does not furnish ${\text{H}}^{+}$ ions in aqueous solutions. Therefore, it does not change its colour.​
$\begin{array}{ccc}\text{subject}& \text{Red litmus}& \text{Blue litmus}\\ \text{Dry}HCI\text{gas}& \text{Red}& \text{Blue}\\ \text{Moistened}N{H}_3\text{gas}& \text{Blue}& \text{Blue}\\ \text{Lemon juice}& \text{Red}& \text{Red}\\ \text{Carbonated soft drink}& \text{Red}& \text{Red}\\ \text{Curd}& \text{Red}& \text{Red}\\ \text{Soap solution}& \text{Blue}& \text{Blue}\end{array}$