Question

An element having atomic number $56$ belongs to :

• A. lanthanides
• B. actinides
• C. alkaline earth metals
• D. none of the above

Answer 1

Answer: (C)

Electronic configuration (atomic number $56$)
$1s^2,2s^2,2p^6,3s^{2}3p^{6}3d^{10},4s^{2}4p^{6}4d^{10}5s^{2}5p^6,6s^2$
The last $2$ electrons are filled in $s$ orbital so the element belong to II group (alkaline earth). As the element contain six shells hence, it belong to sixth period.