Question

The elements A and B obey Newland’s law of the octave. How many elements are there between A and B?
(A) 7
(B) 8
(C) 5
(D) 6

Answer 1

Hint: In the year 1864, the British chemist John Newlands attempted the 62 elements known at that time. The law of octaves states that every eighth element has similar properties when the elements are arranged in the increasing order of their atomic masses.

Complete Solution :
We have been provided that the elements A and B obey Newland’s law of octave,
We need to find out the number of elements between A and B,
The Newlands law of octave is stated as if we organized the chemical elements based on increasing atomic weight, elements which have similar physical and chemical properties are seen after the interval of seven elements.
This can be also written as, If we organize the elements in such an order that their atomic masses go on increasing, then the properties of the first element are similar to the eight-element.
For Example, The eight elements from lithium are sodium. Similarly, eight elements from sodium are potassium.
Therefore, suppose A is the first element and it goes up to element B which is the eight-element. Then there are a total of 6 elements in between elements A and B.

$\text{ H }$	$\text{ Li }$	$\text{ Be }$	$\text{ B }$	$\text{ C }$	$\text{ N }$	$\text{ O }$
$\text{ F }$	$\text{ Na }$	$\text{ Mg }$	$\text{ Al }$	$\text{ Si }$	$\text{ P }$	$\text{ S }$
$\text{ Cl }$	$\text{ K }$	$\text{ Ca }$

Here, lithium$\text{ Li }$, sodium $\text{ Na }$ and potassium $\text{ K }$ have similar physical and chemical properties.
So, the correct answer is “Option D”.

Note: Newland was able to arrange the elements only up to the calcium. It is found that after the calcium element, not every eighth element possesses similar properties as that of the first element. When octave law was stated, there were Only 56 elements known, but several elements were discovered after it.