Question

the atomic numbers of three elements A, B and C are 12, 18 &20 respectively. state, giving reason, which two elements will show similar properties.

Answer 1

Electronic configuration of A,B and c
A, 12 = 2,8,2
B,18 =2,8,8
C,20= 2,8,8,2
Hence, looking at the electronic configuration, A and C have same valency and valence electron, so they both will show similar properties.

Answer 2

according to me
atomic number 12=magnesium
atomic number 20 =calcium
these both lie in same table (alkaline earth metals )
so these two elements show similar properties