Answer:
c. Cr
Explanation:

The compound is containing
ion.
If acid reacts with it, CO_2 evolves.

therefore, Cr would form a precipitate when added to an aqueous solution of this compound. Cr2CO3 is the precipitate.
H.
represents hydrogen element. under non metal classification.
for others, you'll find them under metal element classification.
3 moles of NaOH reacts with 1 mole of phosphoric acid.
<h3>What is the moles ratio of the NaOH and Phosphoric acid reaction?</h3>
The moles ratio of the reaction between NaOH and Phosphoric acid is given by the equation of the reaction below:

Based on the equation of the reaction, 3 moles of NaOH reacts with 1 mole of phosphoric acid.
Learn more about mole ratio at: brainly.com/question/19099163
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As you go from left to right and down to up on the periodic table, atomic radius decreases. This would make helium the smallest and francium the largest.