Answer:
C is the correct answer.
Step-by-step explanation:
In a Ra , Be, Mg is given . These are belong from 2nd group . In moving downwaed to the group no. of shell increase so size of atom increase . S0 the order of these in incresing size is Be<Mg<Ra .
So Be is m=smallest in a .
simillarly order of b in increasing size Si<V<Re .
So Si is smallest .
order of c is Br<As<Se .
These belong from same period an in along the period size decreases due to increase of electrons .