there was a change in its color from white to red which can only be changed by a chemical reaction
answer: it contains 1.0 mole of hcl per 1 liter of solution.
molarity : it is defined as the number of moles of solute present in one liter of solution.
formula used :
n = moles of solute
= volume of solution in liter
thus 1.0 m solution means the solution contain 1 mole in 1 liter of solution.