Question

The law of octaves was proposed by:
A. Newlands
B. Dobereiner
C. Lavoisier
D. Mendeleev

Answer 1

Hint: The term octaves means the interval between the two musical notes, the first note and the eighth note. In the law of octaves, the first element and the eighth element are related to each other in properties. Check the discoveries of each scientist, to know who has given this law.

Complete step by step answer:
Let us discuss the discoveries of scientists in the chemistry given in the options:
A. Newlands: John Newlands put forward his law of octaves in 1864. He noticed that every eighth element had a resemblance with another one when arranged in order of atomic weight. He compared these elements with the octaves of music. The table suggested by Newlands is

sa	re	ga	ma	pa	dha	Ni
(do)	(re)	(mi)	(fa)	(so)	(la)	(ti)
H	Li	Be	B	C	N	O
F	Na	Mg	Al	Si	P	S
Cl	K	Ca	Cr	Ti	Mn	Fe
Co and Ni	Cu	Zn	Y	In	As	Se
Br	Rb	Sr	Ce and La	Zr	-	-

B. Dobereiner: The elements can be classified into groups in the increasing order of atomic masses of three elements called triads. In each triad, the average atomic mass of two elements is equal to the atomic mass of the middle element. Like,

Triads	Atomic masses	Average atomic masses of first and third elements
Lithium $\left( \text{Li} \right)$	6.9	22.95
Sodium $\left( \text{Na} \right)$	23.0
Potassium $\left( \text{K} \right)$	39.0
Calcium $\left( \text{Ca} \right)$	40.1	88.7
Strontium $\left( \text{Sr} \right)$	87.6
Barium $\left( \text{Ba} \right)$	137.3
Chlorine $\left( \text{Cl} \right)$	35.5	81.2
Bromine $\left( \text{Br} \right)$	79.9
Iodine $\left( \text{I} \right)$	126.9

C. Lavoisier: Antoine Lavoisier is known as the father of modern chemistry. He discovered elements like oxygen, carbon, silicon and nitrogen. With the discovery of oxygen, he introduced the term of combustion. He also established the law of conservation of mass and the terms combustion and respiration are related by oxygen.
D. Mendeleev: Dmitri Mendeleev had formulated the Periodic Law and created a far-sighted version of the periodic table. He used the periodic law to predict the properties of eight elements that were yet to be discovered. This contribution to chemistry is still remembered. That’s why he is known as the father of the periodic table. He organised periodic tables along with the symbols to elements on the basis of atomic masses of elements.

The law of octaves was proposed by Newlands, option ‘a’ is correct.

Note: These discoveries had some limitations due to which these were rejected or not followed for long. The limitations are-
(1) Newlands: Applicable up to calcium elements and elements with dissimilar properties are grouped together.
(2) Triads of Dobereiner: Only a few elements were identified in this model. Many elements do not fit into this model.
 (3) Mendeleev: Could not assign the correct position to the hydrogen element.