The element $X$ has the following electron configuration $2, 8, 8, 2$. It means that it belongs to:

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?

Which of the following elements would lose an electron easily?

Properties of the elements are given below. Where would you locate the following elements in the periodic table?
$(a)$ $A$ soft metal stored under kerosene.
$(b)$ An element with variable (more than one) valency stored under water.
$(c)$ An element which is tetravalent and forms the basis of organic chemistry.

Given below are some elements of the modern periodic table. Atomic numbers of the elements are given in the parentheses: $A(4), B(9), C(14), D(19), E(20)$.
$(a)$ Select the element that has one electron in the outermost shell. Also,write the electronic configuration of this element.
$(b)$ Which two elements amongst these belong to the same group? Give reason for your answer.
$(c)$ Which two elements amongst these belong to the same period? Which one of the two has a bigger atomic radius?

Write true or false for the statement: In Mendeleev's periodic table,elements were arranged in the order of their increasing atomic masses and it was also observed that there occurs a periodic recurrence of elements with similar physical and chemical properties.