Calculate the ph of a mixture made by adding 50.0 ml of 0.20 m hcl(aq) to 150.0 ml of water if the temperature of the mixture is 25.0 °c.

PH scale is used to determine how acidic or basic a solution is,
pH can be calculated once the [H⁺] is known.
Here HCl is a strong acid therefore it completely dissociates into H⁺ ions and Cl⁻ ions.
Therefore [HCl] = [H⁺]
number of HCl moles added - 0.20 mol/L x 0.050 L = 0.010 mol
The volume of the final solution = 50.0 + 150.0 = 200.0 mL
then the concentration of HCl = 0.010 mol / 0.200 mL = 0.05 mol/L
therefore [H⁺] = 0.05 M
then pH can be calculated using the following formula,
pH = -log[H⁺]
pH = -log(0.05 M)
pH = 1.30

They are all decomposition reactions.

The answer is c) pyrite