Question

Which of the following set of pairs obeys Newland’s Octave rule?
$A.{\text{ Ne, Na}}$
$B.{\text{. C, N}}$
$C.{\text{. Na, K}}$
$D.{\text{. P, S}}$

Answer 1

Hint : To proceed with this question first let’s understand Newland's Octave rule, he said that if we arrange the known atomic elements in the order of their increasing mass, then every eight element has similar chemical and physical properties.

Complete Step By Step Answer:
This Newland’s Octave rule in $1865$ by an English chemist J.A.R Newlands, he arranged elements on the basis of their increasing atomic weight.
So, looking at our options
Option A – in ${\text{Ne, Na}}$ , the atomic number of neon is ${\text{10}}$ and of sodium is ${\text{11}}$ . So the difference between them is just by ${\text{1}}$ . So, it does not follow octaves rules.
Same as with option b – carbon and nitrogen has differences in their atomic number just by ${\text{1}}$ .
In option C - ${\text{(Na, K)}}$ - Potassium is the eight element from the sodium. So it fits right in with Newland’s Octave rule.
In option D – phosphorus and sulphur have a difference in their atomic number just by ${\text{1}}$ . So, this pair also does not follow Newland’s Octave rule.
Therefore, from the above discussion we can conclude that option C is correct. I.e. ${\text{(Na, K)}}$ follows Newland's Octave rule and has similar chemical and physical properties.

Note :
There were some limitations in Newland's Octave rule - At that time only ${\text{56}}$ elements were discovered and according to his rule only up to calcium, this rule was applicable. Higher elements than calcium disobeyed this rule. Also, his atomic table does not have space for new discovered particles.