Question

Which of the following belongs to the actinides series of elements?
i) \[La\]
ii) \[Lu\]
iii) \[U\]
iv) \[{\text{Sm}}\]

Answer 1

Hint: We need to know that in the world there are a lot of elements in various forms. For study and developing purposes, classification happens. Periodic table used to study the elements in easy form. If one new element is discovered, it means, based on the physical and chemical property we placed in the periodic table.
In general, modern periodic table ordering is based on the atomic number of the atoms. The lowest atomic number starting from the first and followed by a higher atomic number.

Complete answer:
The symbol of uranium is \[{\text{U}}\].
The symbol of samarium is \[{\text{Sm}}\].
The symbol of lutetium is \[{\text{Lu}}\].
The symbol of lanthanum is \[{\text{La}}\].
Out of these four elements, uranium is only one element present in the actinides series of elements.
Therefore, option (C) is correct.

Additional information:
Depending on the energy level of the outermost shell in the atoms, periods are classified and place the atom in respect period. Depending on the electrons shielding and size and physical behaviour of the atom, groups are coming.
In the modern periodic table metallic atoms are placed in the left side of the table and non-metallic atoms are placed in the right side of the table. Metalloids and transition elements are placed in between metal and non-metal elements. Below the two rows are there. There are nothing but lanthanides and actinides. These are f-block elements.

Note:
We need to know that in chemistry, periodic tables play a vital role. Now we are using a modern periodic table. This modern periodic table consists of totally \[118\] elements. In the periodic table there are totally \[18\] columns and \[7\] rows. The columns are called groups. Hence, \[18\] groups in the periodic table. The rows are called periods. Hence, totally \[7\] period in the table.