That would be the first option Ca(OH)2 + H2SO4 → CaSO4 + 2H2O.
The Ca replaces the H2 in H2SO4, and the H2 replaces the Ca is Ca(OH)2.
is the Lewis base in the following reaction:
→ 
<h3>What is lewis base? </h3>
Lewis base is a species that donates an electron pair.
In the above-given chemical equation, the is the lewis base which is donating an electron pair to the central atom of 
to form 
.
Hence, is the Lewis base in the following reaction:
→
Learn more about the lewis base here:
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It depends on the substance,but for most substance it is in the gaseous state.
It is a element.
Pure substances includes either compunds, or elements. Elements are the simplest form of pure substance, they only consist of one kind of atoms. On the other hand, compounds contains two or more elements that are chemically combined together. Although you couldn't separate a compound by physical methods like filtration, but you can seperate them with chemical methods such as heating or electrolysis, using electricity.
Therefore, since compounds can be broken down eventually, so, the answer will be element.
