Mebdeleev's periodic table has helped in correcting the doubtful atomic masses of some elements such as
(i) beryllium (ii) indium
(iii) tellurium (iv) gold

Options

A. `(i),(ii),(iii),(iv)`
B. `(i),(ii)`
C. `(i),(iii)`
D. `(ii),(iii),(iv)`

Answer

A

Explanation

Mendeleev velived that the atomic mass of an elecment may sometimes be amended by a knowledge of those of the adjacent elements. He said that the atomic mass of `Te` cannot be `128` and must lie between `123` and `16`.
Mendeleev also corrected the atomic masses of `Be` (form `13.5` to `9`) and In (for `76` to `114`). Mendeleev argued that tha atomic mass of In taken as `76` would place in-between arsenic, As `(75)`, of group `V` and selenium, `Se (78)`, of group `VI`. As there was no vacant position between `As` and `Se`, Mendeleev suggested that the calculated on the basis of a wrong valency (combining power) of `2`. If the valency of In was charged to `3`, its atomic mass would alter to `114`, putting it in a vacant space between cadmiun `Cd(112)` of group `II` and tin `Sn (118)` of group `IV`. Mendeleev further showed that the compounds of In resembled compounds of `A1` and `T1`, the members of group `III` of the Mendeleev periodic table. He made similar accurate placements for the elements such as uranium `(U)` and beryllium `(Be)`.
He placed gold `(196.2)` after osmiun `(198.6)`, iridium `(197.7)`, and platinum `(197.7)` beliving that the these values were wrong. Mendeleev's prediction based on the chemical properties of these elements was right as the modern values for the atomic masses of these elements are `Os (190.2), Ir(192.2), Pt(195.1)`, and `Au(197.0)`.
Mendeleev was sometimes wrong in assuming that the atomic masses of elements were wrong, but most of his judgments based on chemical properties were correct.