State the Modern Periodic Law.

Which of the following are the characteristics of isotopes of an element?
$(i)$ Isotopes of an element have same atomic masses
$(ii)$ Isotopes of an element have same atomic number
$(iii)$ Isotopes of an element show same physical properties
$(iv)$ Isotopes of an element show same chemical properties

Which of the following elements will form an acidic oxide?

The element with atomic number $14$ is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?

An element $A$ has an atomic number $16$. To which group and period does it belong?

Why are lithium (atomic number $3$) and potassium (atomic number $19$) placed in group $1$? What will be the atomic numbers of the first two elements in group $2$?