The isoelectronic set of ions is

Fluorine,chlorine,bromine and iodine are placed in the same group $(17)$ of the periodic table,because

State whether the following statements are true or false:
$(i)$ As the atomic number increases in a period,the nuclear charge increases,therefore the ionization enthalpy increases.
$(ii)$ As the metallic character of elements increases,the atomic radius generally increases.
$(iii)$ $Mn$ $(Z = 25)$ is a transition element. Although it is a $3d$-orbital element,its position in the periodic table is in the $4^{th}$ period.

Consider the following orders :-
$(I)$ $Li > Na$ (Reducing nature)
$(II)$ $BF_3 > BCl_3 > BBr_3 > BI_3$ (Rate of hydrolysis)
$(III)$ $B > C > N > O > F$ ($1^{st}$ ionization energy)
$(IV)$ $CCl_4 > SiCl_4$ (Boiling point)
The $CORRECT$ order$(s)$ are :-

The electronic configurations of four elements are:
$I. [Xe] \, 6s^1$
$II. [Xe] \, 4f^{14} \, 5d^1 \, 6s^2$
$III. [Ar] \, 4s^2 \, 4p^5$
$IV. [Ar] \, 3d^7 \, 4s^2$
Select the incorrect statement about these elements.

Which of the following statements are correct?
$A.$ The process of the addition of an electron to a neutral gaseous atom is always exothermic.
$B.$ The process of removing an electron from an isolated gaseous atom is always endothermic.
$C.$ The $1^{st}$ ionization energy of boron is less than that of beryllium.
$D.$ The electronegativity of $C$ is $2.5$ in $CH_4$ and $CCl_4$.
$E.$ $Li$ is the most electropositive among elements of group $I$.
Choose the correct answer from the options given below: