Which of the following elements has the highest metallic character?
Element $- IP$

Assertion $(A)$: Boron has a smaller first ionisation enthalpy than beryllium.
Reason $(R)$: The penetration of a $2s$-electron to the nucleus is more than the $2p$-electron; hence,the $2p$-electron is more shielded by the inner core of electrons than $2s$-electrons.

When first ionisation energy is plotted against the atomic number,the peaks in the curve are occupied by

The atomic numbers of elements $X, Y$,and $Z$ are $19, 37$,and $55$ respectively. Which of the following statements is correct?

The correct trend in the first ionization enthalpies of the elements in the $3^{rd}$ period of periodic table is:

What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?