Aqueous environment in a spherical endosome a closed vesicle of 100 nm diameter, is at a pH 5.0, in order to denature and hydrolyze the material internalized by a cell. Assuming Avogadro’s number to be 6 * 10 ^ 23 the number of free protons in an endosome is closest to

(1) 24

(3) 2400

(2) 3

(4) 300

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