Highest density is of $...$.

Approximately what percentage $(\%)$ of the total elements are transition elements?

Identify the general electronic configuration exhibited by the $2^{nd}$ series of transition elements.

$A$ metal $M$ has the electronic configuration $M: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$. To which block does this metal belong?

What is the correct order of atomic/ionic size?

Ferrous ion changes to $X$ ion upon reacting with acidified hydrogen peroxide. The number of $d$-electrons present in $X$ and its magnetic moment (in $BM$) are,respectively: