Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
$(a)$ Classify these elements as metals,non-metals,or metalloids.
$(b)$ How many valence electrons are present in each one of them?

Which of the following sets of elements is written in the order of their increasing metallic character?

Which of the following statement$(s)$ about the Modern Periodic Table are incorrect?
$(i)$ The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number.
$(ii)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses.
$(iii)$ Isotopes are placed in adjoining group$(s)$ in the Periodic Table.
$(iv)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.

Write the atomic numbers of two elements $X$ and $Y$ having electronic configurations $2, 8, 2$ and $2, 8, 6$ respectively.

Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
$F, Na, Mg, Al, Si, P, S, Cl, Ar, K$
$(a)$ Pick two sets of elements which have similar properties.
$(b)$ The given sequence represents which law of classification of elements?

Three elements $A$, $B$, and $C$ have $3$, $4$, and $2$ electrons respectively in their outermost shell. Determine the group number to which they belong in the Modern Periodic Table and state their valencies.