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.

An element which is an essential constituent of all organic compounds belongs to :

Atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ What would be the electronic configuration for each of these elements?
$(b)$ Determine the valency of these elements.

List the anomalies of Mendeleev's periodic table which were resolved by the modern periodic law.

The atomic radii of the elements of the second period are given below:

Second period elements	$B$	$Be$	$O$	$N$	$Li$	$F$	$C$
Atomic Radii $(pm)$	$88$	$111$	$66$	$74$	$152$	$64$	$77$

$(i)$ Arrange these elements in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the periodic table?
$(iii)$ Name the element which has the $(a)$ smallest and $(b)$ largest atomic number.
$(iv)$ From the above data, infer how the atomic size or atomic radius of the elements changes as we move from left to right in a period.
$(v)$ Name one metal, one non-metal, and a metalloid out of these elements.
$(vi)$ Why does atomic radius decrease as we move from left to right in a period?

The atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ Identify the elements.
$(b)$ Identify the group number of these elements in the Periodic Table.
$(c)$ Identify the periods of these elements in the Periodic Table.