What is the $pH$ value for a neutral aqueous solution?

According to the Bronsted-Lowry acid-base theory,which ion is responsible for the acidity of an aqueous solution of an acid?

What happens when metal oxide reacts with water?

$A$ sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the $pH$ paper yellowish-orange. Which of the following would change the colour of this $pH$ paper to greenish-blue?

$500 \ ml$ aqueous solution is prepared by dissolving $2$ moles of $HCl$ in water. What will be the molarity of this solution (in $M$)?

Dry $HCl$ gas does not change the colour of dry blue litmus. Give reason.