Look at the given table and answer: What will be the atomic weight of the middle element in group ‘B’? Group A Element Li ? K Atomic mass 6 . 9 u 23 u 39 . 1 u Group B Element Ca Sr Ba Atomic mass 40 . 1 u ? 137 . 3 u Group C Element Cl Br I Atomic mass 35 . 5 u ? 126 . 9 u

According to Dobereiner's triad the atomic mass of the middle element of the triad is almost equal to the average of the atomic weights of rest of the two elements. Atomic weight of Sr = atomic weight of Ca + atomic weight of Ba 2 Atomic weight of Sr = 40 . 1 u + 137 . 3 u 2 Sr = 177 . 4 u 2 = 88 . 7 u Atomic weight for Sr is 88 . 7 u approximately.

Look at the table and answer: What will be the atomic weight of the element in group ‘C’? Group A Element Li ? K Atomic mass 6 . 9 u 23 u 39 . 1 u Group B Element Ca Sr Ba Atomic mass 40 . 1 u ? 137 . 3 u Group C Element Cl Br I Atomic mass 35 . 5 u ? 126 . 9 u

According to the law of triad proposed by Dobereiner, the atomic mass of the middle element of the triad is almost equal to the average of the atomic weights of rest of the two elements. Atomic weight of Br = atomic weight of Cl + atomic weight of I 2 Atomic weight of Br = 35 . 5 u + 126 . 9 u 2 Br = 162 . 4 u 2 = 81 . 2 u Atomic weight for Br is 81 . 2 u approximately.

EASY

10th Chhattisgarh Board

IMPORTANT

Earn 100

Look at the given table and answer:

Which element will lie in the middle of group ‘A’?

Group A Element $Li$ $?$ $K$

Atomic mass $6.9$ $23$ $39.1$

Group B Element $Ca$ $Sr$ $Ba$

Atomic mass $40.1$ $?$ $137.3$

Group C Element $Cl$ $Br$ $I$

Atomic mass $35.5$ $?$ $126.9$

Important Questions on Periodic Classification of Elements

EASY

10th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-10>Chapter 4 - Periodic Classification of Elements>Questions>Q 1

Look at the given table and answer:

What will be the atomic weight of the middle element in group ‘B’?

Group A	Element	$Li$	$?$	$K$
Group A	Atomic mass	$6.9 u$	$23 u$	$39.1 u$
Group B	Element	$Ca$	$Sr$	$Ba$
Group B	Atomic mass	$40.1 u$	$?$	$137.3 u$
Group C	Element	$Cl$	$Br$	$I$
Group C	Atomic mass	$35.5 u$	$?$	$126.9 u$

EASY

10th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-10>Chapter 4 - Periodic Classification of Elements>Questions>Q 1

Look at the table and answer:

What will be the atomic weight of the element in group ‘C’?

Group A	Element	$Li$	$?$	$K$
Group A	Atomic mass	$6.9 u$	$23 u$	$39.1 u$
Group B	Element	$Ca$	$Sr$	$Ba$
Group B	Atomic mass	$40.1 u$	$?$	$137.3 u$
Group C	Element	$Cl$	$Br$	$I$
Group C	Atomic mass	$35.5 u$	$?$	$126.9 u$