Explain the trends in chemical reactivity and properties across the periodic table.

(N/A) $1$. In a group,the increase in atomic and ionic radii with an increase in atomic number generally results in a gradual decrease in ionization enthalpies.
$2$. The metallic character increases down the group,while non-metallic character decreases.
$3$. These trends are related to the reducing and oxidizing properties of the elements.
$4$. In the case of transition elements,a reverse trend is often observed due to the complex nature of atomic size and ionization enthalpy variations.