Explanation
Sodium hexa meta phosphate $$Na_6(PO_3)_6$$ or $$Na_6P_6O_{18}$$ is called Calgon. It is used for softening hard water. Calgon ionizes to give a complex anion: The addition of Calgon to hard water causes the calcium and magnesium ions of hard water to displace sodium ions from the anion of Calgon. This results in the removal of calcium and magnesium ions from hard water in the form of a complex with Calgon. The water is softened and sodium ions are released into the water.
$$Na_2[Na_4(PO_3)_6] + 2Ca^{2+} \rightarrow Na_2[Ca_2(PO_3)₆_6+ 4Na^{+}$$.
Hence option A is correct.
Beryllium and magnesium do not give any colour to the flame test because they have a small size and very high ionization enthalpies. The energy of the flame is not sufficient to excite the electrons to higher energy levels. Hence, they do not impart any characteristic colour to the flame.
Li differs from the rest of the family members and shows anomalous behaviour. Lithium bicarbonate found in solution form while other bicarbonates of alkali metals exist in solid-state. Its anomalous behaviour is due to the following reasons:-
1.Its exceptionally small size2.High polarizing power.
So $$LiHCO_3$$ does not exist in solid-state.
$$LiHCO_3$$ is found in solution(aqueous) form while rest alkali metals hydrogen carbonates are solid due to the anomalous properties of Li and it's diagonal relationship with the Mg.
Following are the points of difference between Li and other alkali metals.
(i) it's exceptionally small size.
(ii)it's high polarizing power(charge/radius ratio).
$$Mg$$ is present in chlorophyll which is a green pigment and is used in photosynthesis in green plants.
Hence option B is correct.
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