Verified Answer :

Willchemistry

Molar mass:

HF = 1 + 19 = 20.0 g/mol

Number of moles :

124 / 20.0 =>  6.2 moles

Volume = 2.4 L

M = n / V

M = 6.2 / 2.4

M = 2.6 M

Answer A

hope this helps!

JoshEast

The Answer is A as you said:

Molarity = \(\frac{no. of moles}{volume}\)

moles of HF = \(\frac{mass}{molar mass}\)
                    = \(\frac{124}{(1 + 19)}\)
                    = 6.2 mol

∴  molarity of HF = \(\frac{6.2 mol}{2.4 dm^{3} }\)
                           = 2.58 M
                           ≈ 2.6 M