Answer
All the statements are justified, the correct answer is d. all the above statements are correct.
Work Step by Step
In the periodic table, the atoms are arranged according to their atomic number. The rows are called periods and columns are called groups. In a period from left to right, the atomic number of every atom is increased by one unit.
Each atom in the periodic table has its atomic number on its top, and its mass number below the atom symbol. Hence, option a is correct.
The period number to which an atom belongs is equal to the number of shells in the atom. Thus, the option c is also correct.
The electrons revolve around the nucleus in definite paths. The lower energy shells must be filled with the electrons; gradually, the next higher energy levels will be filled.
The first shell is filled with two electrons, second shells are filled with 8 electrons, the third shell is filled with 8 electrons and the fourth shell is filled with 18 electrons, and so on. the outer most shell of an atom is called valence shell. Generally, the number of the outer most shell will be the period to which an atom belongs. The number of electrons present in valence shell is equal to its group number. The group number of the atom is equal to electrons in the outer shell or valence shell.
So option c is right.
