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Add proton + neutrons = Mass 37
Proton is same as your atomic mass= 17
If you go on the periodic table look up 17 and it will give u the letter.
Explanation:
(a) potassium oxide with water

According to reaction,1 mole of potassium oxide reacts with 1 mole of water to give 1 mole of potassium hydroxide.
(b) diphosphorus trioxide with water

According to reaction,1 mole of diphosphorus trioxide reacts with 2 moles of water to give 2 moles of phosphorus acid.
(c) chromium(III) oxide with dilute hydrochloric acid,

According to reaction,1 mole of chromium(III) oxide reacts with 6 moles of hydrochloric acid to give 2 moles of chromium(III) chloride and 3 moles of water.
(d) selenium dioxide with aqueous potassium hydroxide

According to reaction,1 mole of selenium dioxide reacts with 2 moles of potassium hydroxide to give 1 mole of potassium selenite and 1 mole of water.
Answer: since the sodium ion is Na+, and sulfate is SO4(2-), you'll need 2 sodiums for a sulfate, making sodium sulfate Na2SO4.
Explanation:
Oxygen and Sulfur are in the same group.
Sulfur is the next element in the group, and it reacts with hydrogen gas (H2) in a manner similar to oxygen.