Means that 100 ml soln contains 5.8 g of nacl. Considering it to be dilute and neglecting vol of nacl we take 100 ml soln=100ml water=100g water
See the molality of the soln is 1m. Now multiply it by i=2 we get 2.. Same as that for option b.
I think if molality is same then mol fraction will alaso be same.