Question

an atom contains 70 protons, 70 electrons, and 99 neutrons. what is the mass number?
239
169
140
70
hypothetical element q has 3 isotopes with the relative abundances shown in this table. what is the average atomic mass of element q?
isotopes of element q
isotope atomic mass (amu) relative abundance (%)
1 53 80 %
2 56 15%
3 58 5%
a. 55.7
b. 56.0
c. 33.3
d. 53.7

Explanation:

Step1: Mass number = protons + neutrons

$70 + 99 = 169$

Step1: Calculate each isotope's contribution

$53 \times 0.8 = 42.4$, $56 \times 0.15 = 8.4$, $58 \times 0.05 = 2.9$

Step2: Sum contributions for average mass

$42.4 + 8.4 + 2.9 = 53.7$

Answer:

169