Which property of water is unchanged when a small quantity of sodium chloride is added to it

Answer is: color.

Chemical reaction of dissociation of sodium chloride in water:

NaCl(aq) → Na⁺(aq) + Cl⁻(aq).

Small quantities of water are colorless, solution of sodium chloride is also colorless.

Adding sodium chloride to water change water melting and boiling points.

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2