Formula unit mass for ${K_2}C{O_3}$ is.
A) \[140\]
B) \[138\].
C) \[120\].
D) \[125\].

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Hint:We know that Mass is both a property of an actual body and a proportion of its protection from speeding up (an adjustment in its condition of movement) when a net power is applied. An article's mass likewise decides the strength of its gravitational fascination in other bodies. The essential SI unit of mass is the kilogram. In material science, mass isn't equivalent to weight, despite the fact that mass is regularly dictated by estimating the item's weight utilizing a spring scale, as opposed to adjusting scale contrasting it straightforwardly and known masses.

Complete step by step answer:
We have to remember that a nuclear unit of mass is characterized as precisely 1/12 the mass of a carbon-12 particle. The carbon-12 particle has six neutrons and six protons in its core. The nuclear unit mass is represented as AMU or amu.
$1AMU = {\text{Average of the proton rest mass and the neutron rest mass}}$
$1AMU = 1.67377 \times {10^{ - 27}}{\text{kilogram}}$ or $1.67377 \times {10^{ - 24}}gram$
The meaning of molecular weight is most definitely inseparable from sub-atomic mass; nonetheless, in like manner practice, it is likewise exceptionally factor similar to the units utilized related to it. Numerous basic preliminary sources use \[g/mol\] and viably characterize it as an equivalent of molar mass.
The formula unit mass of ${K_2}C{O_3}$
$ = 2 \times {\text{atomic mass of K}} + {\text{Atomic mass of carbon}} \times {\text{Atomic mass of oxygen}}$
On substituting the known values we get,
\[ = 2 \times 39 + 1 \times 12 + 3 \times 16\]
On simplification we get,
$ = 138u$
Hence option B is correct.

Note:
We need to know that the contrast among mass and weight is that mass is the amount of issue that is contained in an article. It is a consistent amount estimated in kilograms and is a scalar quantity. Whereas weight is the power with which an item gets pulled towards the earth. It's anything but a steady amount estimated in Newton and is a vector amount.