What is the concentration of a solution that was made by diluting 1 ML of 6 M HCL to 15 ML

The concentration of the solution is 0,4M

Explanation:

We use the formula

C initial x V initial = C final x V final

6 M x 1 ml = C final x 15 ml

C final = (6 M x 1 ml) / 15 ml = 0, 4 M

(This formula applies to liquid solutions)