Question

Is the common salt is similar to the salt for fast (vrat ka namak)? If it's components differ in any way then please tell me its formula? Is it iodised?

Answer 1

In truth, not much.  The primary ingredient to both, not surprisingly, is sodium chloride.  In fact, the U.S. government requires that any food-grade salt be a minimum of 97.5% pure, so any type of salt you consume in the U.S. (and most developed countries) is going to be almost exactly the same as any other type of salt in terms of what it is made up of.

However,  “Regular” or “table” salt does usually contain an anti-clumping agent, like calcium silicate or sodium ferrocyanide, and iodine (see Why Iodine is Added to Salt).  Kosher salt usually doesn’t contain either of these things, though occasionally some manufacturers do put an anti-clumping agent in. But this is rare and even when they do, it’s usually much less than is in table salt.