Question

The law of triads is not applicable to :

• A. $Os,Ir,Pt$
• B. $Ca,Sr,Ba$
• C. $Fe,Co,Ni$
• D. $Ru,Rh,Pt$

Answer 1

Answer: (C), (D)

The correct options are
C $Fe,Co,Ni$
D $Ru,Rh,Pt$

The law of triads does not apply to $Ru,Rh,Pt$.

According to the law of triads, the atomic weight of the middle element is approximately equal to the arithmetic mean of the other two elements.

The atomic weights of $Ru,Rh$ and $Pt$ are $101,102.9$ and $195$ respectively.

The arithmetic mean of the atomic weights of $Ru$ and $Pt$ is $\frac{101+195}{2}=148$
Hence, the atomic weight of $Rh$ is not equal to the arithmetic mean of the atomic weights of $Ru$ and $Pt$.

$Fe=56,Co=59$ and $Ni=59$

Mean of the weights of $Fe$ and $N$i is not equal to the weight of $Co$.

Hence, the correct options are $\text{C}$ and $\text{D}$