A sample contains 200 atoms of hydrogen, 0.05 gm atom of nitrogen, 1020 gm atom of oxygen. What is the approximate no. of total atoms

This question uses atomic structure & atomic mass, mole concept & particle counting. Convert all given quantities into moles using n = given amount/molar mass, use Avogadro's number where needed to get particles, and then compare with the options; this matches option C.