The correct options are
A Boron is a rare element.
C B exist in two isotopic form, 10B and 11B
Boron is a rare element. It occurs as H3BO3,Na2B4O7.10H2O,Na2B4O7.4H2O.
It has two isotopic form, 10B and 11B.
Aluminium is the most abundant metal and it occurs as Al2O3.2H2O and Na3AlF6
Therefore, the correct statementrs are (a) and (c).