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Sodium Chromate (Na2CrO4) is made commercially by:
A.Heating mixture of Cr2O3 and Na2CO3
B.Heating mixture of chromite ore and sodium carbonate in the presence of oxygen
C.Heating sodium dichromate with sodium carbonate
D.Reacting NaOH with chromic acid

Answer
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Hint: We have to know that the sodium Chromate (Na2CrO4) is a yellow hygroscopic compound and an intermediate in the extraction of chromium from its ores. Chromite (iron chromium oxide),FeCr2O4, is the most important chromium ore mineral. This is an oxide mineral. Chromium ores are used for preparing chromate salts.

Complete step by step solution:
We have to remember that the sodium Chromate (Na2CrO4) is made commercially by heating a mixture of chromite ore and sodium carbonate in the presence of oxygen in a reverberatory furnace and liberates carbon dioxide.
We can write the chemical reaction for sodium chromate (Na2CrO4) preparation as,
4Fe(CrO2)2+8Na2CO3+7O2Δ8Na2CrO4+2Fe2O3+8CO2
This reaction converts chromium into chromates, leaving behind chromium ores.
Therefore, the option B is correct. (Heating mixture of chromite ore and sodium carbonate in the presence of oxygen)
In industries, we need to prepare a large amount of sodium chromate by the reaction of chromium oxide with sodium carbonate.
The chemical reaction for the vast scale preparation of sodium chromate by the reaction of Chromium(III)Oxide Cr2O3, roasting with sodium carbonate, Na2CO3.
2Cr2O3+4Na2CO3+3O24Na2CrO4+4CO2
In the above reaction Chromium(III)Oxide roasting with sodium carbonate,Na2CO3, in the presence of air.
Therefore, the option A is also correct.
Therefore, the option A and B is correct.

Note: We have to remember that the chromite is a mineral, it is also used to prepare other chromates. When sodium hydroxide, chromite ore and sodium nitrates are used for preparing sodium chromate in another method, subsequent to its formation, sodium dichromate is obtained by the conversion of chromate salt.
We have to know that the sodium chromate is used for conversion of primary and secondary alcohols to carboxylic acids and ketones respectively in organic chemistry. Also it is used in the petroleum industry for corrosion inhibitors.