Question

what element with a mass number of 100 has 56 neutrons in its nucleus? answer: a fermium (fm) b ruthenium (ru) c barium (ba) d copernicium (cn) e radium (ra)

Explanation:

Step1: Recall mass - number formula

The mass number ($A$) is the sum of the number of protons ($p$) and neutrons ($n$), i.e., $A=p + n$.

Step2: Calculate number of protons

Given $A = 100$ and $n=56$. We can find the number of protons $p$ by rearranging the formula: $p=A - n$. So, $p=100 - 56=44$.

Step3: Identify element by atomic number

The atomic number of an element is equal to the number of protons. The element with atomic number 44 is ruthenium (Ru).

Answer:

B. ruthenium (Ru)