Question

The correct arrangement of decreasing order of atomic radius among $Na,K,Mg$ and $Rb$ is

• A. $Rb>Na>K>Mg$
• B. $K>Rb>Na>Mg$
• C. $Rb>K>Na>Mg$
• D. $Mg>Rb>K>Na$

Answer 1

Answer: (C)

$Na,K$ and $Rb$ are of group $1$ elements and size increase down the group $1$ elements $(v)$.
$Na$ and $Mg$ are of group $1$ and $2$ elements respectively but both belong to $3$ rd period. Along the period size decreases $(\to ),$ i.e. size of $Na>Mg$.
Hence the order of sizes is