Answer: a. It receives a hydrogen ion.
Explanation: Base is a species which is capable of donating its negative quantity and accepting the positive one.
For example, ammonia is considered as a base because it is capable of donating its lone pairs of electrons and can accept an proton as well.
Here, out of the given options, Hydrogen 
is a proton which is acting as a positive species and hydroxide ion 
is a negative species.
Thus, option (A) is the correct answer as it will receive a hydrogen ion from another base making itself a conjugate acid.
Answer:
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An ion has a positive or negative charge. While a covalent bond always has no charge, meaning it is neutral.
As we move down the group, the metallic bond becomes more stable and the formation of forming covalent bond decreases down the group due to the large size of elements.
Covalent and metallic bonding leads to higher melting points. Due to a decrease in attractive forces from carbon to lead there is a drop in melting point.
Carbon forms large covalent molecules than silicon and hence has a higher melting point than silicon.
Similarly, Ge also forms a large number of covalent bonds and has a smaller size as compared to that of Sn. Hence melting point decreases from Ge to Sn.
The order will be C>Si>Ge>Pb>Sn.
To learn more about the covalent bond, visit: brainly.com/question/10777799
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Temperature is a measure of "Molecular movement"
In short, Your Answer would be Option B
Hope this helps!
