Which definition best describes a base?
a. a substance in a solution that releases hydrogen ions and lowers the ph
b. a substance in a solution that captures hydrogen ions and raises the ph
c. a substance in a solution that releases and captures hydrogen ions, keeping the ph the same
d. a substance in a solution that provides color over a narrow range of ph

The correct answer is:

B. A substance in a solution that captures hydrogen ions and raises the pH

Explanation:

Bases are substances that, in aqueous solution, release hydroxide (OH−) ions, are smooth to the touch, can taste bitter if an alkali,[1] change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, increase particular chemical reactions (base catalysis), receive protons from any proton donor, and/or contain completely or partially displaceable OH− ions

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.