Question

list mole is si unit for amount of substance .define it wuth examples

Answer 1

I think mass ..........

Answer 2

According to the BIPM and Wikipedia, "amount of substance" (as measured in moles) is one of the base quantities in our system of weights and measures. Why?

I get why the MOLE is useful as a unit. In fact, my question isn't really about the mole at all; I just mention it because what little information I could find generally talked about moles, not about "amount of substance". Nor am I asking about why it's chosen as a base quantity and not a derived quantity. I get that any particular choice of bases is more or less arbitrary.

I don't understand why it's a dimensional quantity at all. It is, after all, just a count of things; every student is taught to think of it as "like 'a dozen', only more sciencey". Can't we just call it a dimensionless number?

No, says SI; molar mass doesn't just have dimensions of MM, it has dimensions of M⋅N−1M⋅N−1; and Avogadro's number isn't just a number, it's got units of "per mole" (or dimensions of N−1N−1).

Contrast this with an "actual" dimensionless quantity, plane angle (and its unit the radian). Now, you might say that it's dimensionless because radians are defined as arc length over radius, and so plane angle is just L⋅L−1L⋅L−1; cancel out and you have no dimensions. That strikes me as arbitrary. We could just as easily argue that arc length is "really" a quantity of a⋅La⋅L (where aa is plane angle), because it's the measurement of a quantity that subtends aa at distance LL.