The scientist who showed that the atomic number of an element is a more fundamental property than its atomic mass is:

An element $X$,which is a yellow solid at room temperature,shows catenation and allotropy. $X$ forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are major air pollutants.
$(a)$ What would be the nature (acidic/basic) of the oxides formed?
$(b)$ Locate the position of the element in the Modern Periodic Table.

An element $X$ belongs to the $3rd$ period and group $13$ of the Modern Periodic Table.
$(a)$ Determine the valence electrons and the valency of $X$.
$(b)$ Determine the molecular formula of the compound formed when $X$ reacts with an element $Y$ (atomic number $= 8$).
$(c)$ Write the name and formula of the compound formed when $X$ combines with chlorine.

Which element has
$(a)$ a total of three shells,with four electrons in its valence shell?
$(b)$ a total of two shells,with three electrons in its valence shell?
$(c)$ twice as many electrons in its second shell as in its first shell?

Which of the given elements $A, B, C, D$ and $E$ with atomic numbers $2, 3, 7, 10$ and $30$ respectively belong to the same period?

How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?