The atomic number of an element is 12. State whether its oxide is acidic or basic.

State the basis of classification of elements in the Modern Periodic Table.

Two elements X and Y have atomic numbers 10 and 14 respectively. Identify the group numbers of these elements in the periodic table.

List any two properties of the elements belonging to the first group of the Modern Periodic Table.

Why are isotopes of an element having different atomic masses placed at the same position in the periodic Table?

Write two elements for each of the following: i. Alkali metals, ii. Noble gases.

Account for the following:

a. Cations are smaller in size than the corresponding atom.

b. The noble gases were discovered very late.

The electronic configuration of four elements A,B,C and D is given as follows:

A-2,8 B-2,8,1

C-2,8,2 D-2,8,8

a. Which of them belong to the same period? Name the period.

b. Which of them belong to the same group? Name the group.

In Mendeleev’s Periodic Table the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.

Write two points of differences between Mendeleev’s Periodic Table and the Modern Periodic Table.

“Hydrogen occupies a unique position in Modern Periodic Table.” Justify the statement.

Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period, and (ii) down a group? Give reason to justify your answer.

Four elements A,B,C, and D have atomic numbers 12, 13, 14 and 15 respectively.

Answer the following questions giving reasons:

a. What is the number of valence electrons and valency of D?

b. Which of them will have largest atomic radii?

C. which of these elements will form the most basic oxide?

An element A on combining with O₂ produces an oxide A₂O which is basic in nature.

a. How many electrons must be there in the outermost shell of the element A?

b. To which group of periodic table it belongs?

c. Identify whether it is a metal or non-metal.

An element ‘X’ belongs to 3^rd period and group 16 of the Modern Periodic Table.

a. Determine the number of valence electrons and the valency of ‘X’.

b. Molecular formula of the compound when ‘X’ reacts with hydrogen and write its electron dot structure.

c. Name the element ‘X’ and state whether it is metallic or non-metallic.

An element ‘X’ (Atomic number = 20) burns in the presence of oxygen to form a basic oxide.

a. Identify the element and write its electronic configuration.

b. State its group number and period number in the Modern Periodic Table.

C. Write a balanced chemical equation for the reaction when this oxide is dissolved in water.

How does the tendency of the elements to lose electrons change in the Modern Periodic Table in

a. a group

b. a period and why?

The elements of a period of the periodic table are given in order from left to right with one of its element missing:

a. To which period do these elements belong?

b. One element of this period is missing. Which is the missing element and where should it be placed?

c. Which one of these elements in this period shows the property of catenation?

d. Which one of these elements is least reactive?

The position of some elements A,B,C,D,E,F and G in the Modern Periodic Table is given as under:

a. In which group are inert elements placed?

b. What type of ions would B, C, E and F form?

c. Which elements would have chemical properties similar to C?

d. How many shells would A have?

e. What is the similarity between A and D?

f. Identify the most abundant element in the earth’s crust.

a. The following is a list of the electron distributions of atoms of unknown elements.

Choose an element from the list for each of the following descriptions.

i. It is a noble gas.

ii. It is a soft metal with a low density.

iii. It has giant covalent structure similar to diamond.

iv. It can form a negative ion of the type X^3-.

b. How does electronic configurations of atoms change in a period with increase in atomic number?