At what $pH$ is rain water said to be acidic?

Name the gas evolved when dilute $HCl$ reacts with sodium hydrogen carbonate. How is it recognized?

Give the chemical name and formula of:
$(i)$ Soda ash
$(ii)$ Blue vitriol
$(iii)$ Baking soda

What will be the value of $pH$ if blue litmus paper turns red in an aqueous solution?

Which of the following cannot be used as an antacid for the treatment of acidity?

Name the acid present in ant sting and give its chemical formula. Also,suggest a common method to get relief from the discomfort caused by the ant sting.