Observe the following statements:
$I$. The physical and chemical properties of elements are periodic functions of their electronic configuration.
$II$. Electronegativity of fluorine is less than the electronegativity of chlorine.
$III$. Electropositive nature decreases from top to bottom in a group.
The correct answer is:

The first element of a group differs in many ways from the other heavier members of the group due to:

Consider the following elements arranged in a periodic table segment as shown in the image.
Which of the following is/are true about $A^{\prime}, B^{\prime}, C^{\prime}$ and $D^{\prime}$?
$A$. Order of atomic radii: $B^{\prime} < A^{\prime} < D^{\prime} < C^{\prime}$
$B$. Order of metallic character: $B^{\prime} < A^{\prime} < D^{\prime} < C^{\prime}$
$C$. Size of the element: $D^{\prime} < C^{\prime} < B^{\prime} < A^{\prime}$
$D$. Order of ionic radii: $B^{\prime+} < A^{\prime+} < D^{\prime+} < C^{\prime+}$
Choose the correct answer from the options given below:

$X$,$Y$,and $Z$ are elements of the same period and belong to the $p$-block. $Y$ has a positive value of $\Delta_{eg}H$ (electron gain enthalpy),and $Z$ has the highest $2^{nd}$ ionization energy $(I.E.)$ among them. What is the correct order of their atomic numbers?
$(a)$ $X < Y < Z$
$(b)$ $X < Z < Y$
$(c)$ $Y < Z < X$
$(d)$ $Z < Y < X$

Which of the following orders is incorrect?

Fill in the blanks:
$(i)$ Atoms and ions having the same number of electrons are known as ........... .
$(ii)$ The quantitative measure of the tendency of an element to lose an electron is called ........... .
$(iii)$ The screening effect is also known by the name ........... .
$(iv)$ The enthalpy change when a gaseous neutral atom forms a negative ion is called ........... .