True False Science Class 10 Chapter 5 Periodic Classification of Elements

Read the following statements and write your answer as true of false.:

Question.1.
When Mendeleev started his work, 63 elements were known.

Question.2.
Dobereiner could identify only three triads of elements.
These are: Li, Na, K; Ca, Sr, Ba and Cl, Br, I.

Question.3.
Elements are classified on the basis of similarities in their properties.

Question.4.
Rows in the periodic table are called periods.

True

Explanation: Rows in the periodic table are called periods. The columns of the periodic table are called groups.

Question.5.
The columns of the periodic table are called groups.

Question.6.
You will find metals on the extreme right side of the periodic table.

False

Explanation: Inert gases are found on the far right of the periodic table. Halogens are in the second group form the right. Metals of all types are found around the left and middle side of the periodic table. There may be alkali, transition, or alkaline earth metals across the table.

Question.7.
Although the order of elements is based on atomic number, vertical families share similar chemical properties.

Question.8.
As nuclear charge increases, atomic orbitals become smaller and more stable.

Question.9.
Noble gases are placed extremely left in the periodic table.

False

Explanation: Noble gases are placed extremely right in the periodic table.

Question.10.
Magnesium is more metallic in nature than sodium.

False

Question.11.
As number of shells increases, atomic orbitals become larger and less stable.

Question.12.
Atomic radii decrease from left to right across a row of the periodic table.

Question.13.
Atomic radii increase from top to bottom down a column of the periodic table.

Question.14.
Fluorine has highest electron affinity in the periodic table.

Question.15.
Valency changes down the group.

False

Question.16.
The elements of group 17 are called halogens.

Question.17.
Along a period, acidic character of the oxide of the elements increases and their basic character decreases.

Question.18.
The elements X with atomic number 15 belongs to third period and group 15.

Question.19.
The number of shells increases in a given period from left to right in the periodic table.

False

Explanation: The number of shells remain same in a given period.

Question.20.
The elements silicon, germanium and arsenic are called metalloids.

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