Q.21)-The mass number of a nucleus is
  • always less than its atomic number
  • the sum of the number of protons and neutrons present in the nucleus
  • always more than the atomic weight
  • a fraction
Q.22)-The hydronium ion is
  • H+
  • HO -
  • H2+
  • H3O+
Q.23)-The most electropositive elements among the following is
  • Na
  • Ca
  • K
  • Cs
Q.24)-The method that cannot be used for removing permanent hardness of water is
  • adding sodium carbonate
  • distillation
  • adding caustic soda
  • boiling
Q.25)-Zone refining is used for the purification of
  • Au
  • Ge
  • Ag
  • Cu
Q.26)-The high reactivity of fluorine is due to
  • its high electro negativity
  • small size of fluorine atom
  • availability of d-orbitals
  • strong F - F bond
Q.27)-The major constituent of air is
  • nitrogen
  • carbon dioxide
  • oxygen
  • hydrogen
Q.28)-The main chemical constituent of clay is
  • silicon oxide
  • aluminium borosilicate
  • zeolites
  • aluminium silicate
Q.29)-The mineral containing both magnesium and calcium is
  • magnesite
  • calcite
  • carnallite
  • dolomite
Q.30)-The main active constituent of tea and coffee is
  • nicotine
  • chlorophyll
  • caffeine
  • aspirin