Question

how to learn mass no. of periodic table {first 30}​

Answer 1

The atomic number of the element × 2 that will gives you the atomic mass of the element except H,Al,Cl,Ar,Be and mainly K upto 20 elements and we have to add (2 or 3 or 4 or 5) to the multiplied atomic number with 2 for the atomic number 21 to 30.