I have heard that cooking bengal gram with salt can lead to increased cooking time compared to cooking it without salt.So i used to add salt just before serving the curry.Other pulses like green gram are cooked with salt without any noticeable similar problems of delayed softening. Is this problem about bengal gram or chickpea is true?If so why is it so?
No, this is a common myth. If you want to test it, you don't "try once with salt", you divide the same batch of beans and cook them both, one with salt and one without, under the same conditions, and repeat. This is what a food author did, although he seems to not have repeated the experiment: http://www.seriouseats.com/2016/09/salt-beans-cooking-soaking-water-good-or-bad.html. His salted beans were somewhat better than the unsalted, and he states he now always cooks them in salted water.
I don't think this is true. If anything, salt would help the bengal gram (chickpea or garbanzo bean) soften sooner because it would absorb moisture more easily and therefore soften sooner.
If you soak the bengal gram overnight (you should for taste/texture/ease of cooking) then salting during the soak would definitely not cause an increase cooking time, as once again they will contain more water and therefore cook faster.