How many atoms are there in 3.4 g of ammonia, NH3\mathrm{NH_{3}}NH3?
Relative atomic mass (ArA_rAr): H = 1.0 N = 14.0
The Avogadro constant is 6.02 × 1023.
1.20×10231.20\times10^{23}1.20×1023
3.61×10233.61\times10^{23}3.61×1023
4.82×10234.82\times10^{23}4.82×1023
2.05×10242.05\times10^{24}2.05×1024
134 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.