Question

how 1 amu is equivalent to gram/mole

Answer 1

Chemists measure macroscopic quantities of atoms in units called moles. By definition, a mole is the number of atoms in exactly 12 grams of carbon-12. That number turns out to be Avogadro's number, which is 6.022 x 1023. This creates a relationship between the atomic mass and macroscopic weight of every element. For any element, its atomic mass in AMU is equal to the weight of 1 mole of the element in grams. For example, all natural isotopes of oxygen collectively have an atomic mass of 15.999 AMU, so one mole of oxygen weighs exactly 15.999 grams. Similarly, one mole of hydrogen weighs 1.008 gram, because the collective atomic mass of all isotopes of hydrogen is 1.008 AMU.