A counter advances once for each distinct proton count represented by an element in period 1. A learner guesses 8 and another guesses 18. How many advances does it actually make? Enter the number.

Объяснение

Period 1 contains two elements, so it represents two distinct proton counts and the counter advances twice. The guesses 8 and 18 import unrelated table counts rather than using the size of this row.