The atomic number of two elements are given below: 

$11,15$ 

Determine the valency of these elements. 

Arrange the following in order of increasing atomic radius

$\mathrm{Li},\mathrm{Be},\mathrm{F},\mathrm{N}$

Arrange the following in order of increasing atomic radius

$\mathrm{Cl},\mathrm{F},\mathrm{Br},\mathrm{I}$

Arrange the following in order of increasing metallic character

$\mathrm{Mg},\mathrm{Ca},\mathrm{K},\mathrm{Ge},\mathrm{Ga}$

Rewrite the following statement in a correct form after correction, if necessary. 

Periods are horizontal rows of elements. 

Rewrite the following statement in a correct form after correction, if necessary. 

Groups have elements with consecutive atomic numbers. 

Rewrite the following statement in a correct form after correction, if necessary. 

Elements in the same period have equal valency. 

In the Modern Periodic Table, the element calcium (atomic number $=20$) is surrounded by elements with atomic numbers $12,19,21$ and $38$. Which of these elements have chemical properties resembling calcium and why? Identify the element which is more metallic as compared to calcium.