Answer:
In both cases, the gas evolved is H2. When calcium reacts with water the heat evolved is not suffcient for hydrogen to catch fire. On the other hand, sodium metal reacts with water violently and in this case a lot of heat is evolved which is sufficient for hydrogen to catch fire.
Explanation:
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The correct option is B.
To determine the formula of a new substance, one has to first determine the percentage composition of each of the elements in the compound. The ratios of each element in the compound will give information about how much of each element is present. The formula of the element will be given based on the quantity of each constituent in the compound.