The letter ‘p’ in pH stands for ‘potenz’ which in German means ______.

Concept

A scientific symbol is often an abbreviation of an ordinary word in the language of the scientist who coined it, so decoding the symbol means translating that word rather than expanding it into a same-letter English term. This is why a letter in a chemical notation can carry a meaning that has nothing to do with the chemistry it is used for.

Application

S. P. L. Sørensen introduced the pH scale in 1909 and defined it as pH = −log10[H+]. Standard chemistry syllabi explain the leading letter as an abbreviation of the German noun ‘Potenz’, and the English translation of ‘Potenz’ is “power” — in ordinary German it carries the sense of strength or capability, and in mathematics it names the power (index) to which a base is raised. On that reading pH is spoken of as the “power of hydrogen”; NCERT Class 10 Science, ‘Acids, Bases and Salts’, glosses the letter exactly so, and its Hindi edition gives ‘शक्ति’. Sørensen’s own 1909 paper does not record why he picked the letter, so this reading is a textbook convention rather than a documented intention — but it is the convention this question is set on, and the word that completes the sentence is “power”.

Cross-check

Translating each of the other candidate words back into German shows that none of them is what ‘Potenz’ says:

• “Proton” is ‘Proton’ in German as well — the name of the positively charged particle an acid releases in solution, not a translation of ‘Potenz’.

• “Potential” is the look-alike trap: German writes that quantity as ‘Potenzial’ (or ‘Potential’), a different word naming the electric or electrode potential of a point, i.e. potential energy per unit charge.

• “Percent” is ‘Prozent’ in German — an arithmetic proportion out of a hundred, again a different word.

Only “power” is the English translation of ‘Potenz’, which fixes it as the correct completion.