Answer: the rarest element is Francium. J is not on the periodic table. also Dmitri Mendeleev proposed the periodic table.
Explanation: Kinda looked the last one up.
The atomic number tells you the number of protons in an atom. This value never changes because the number of protons in the nucleus always remains constant. The mass number tells you the number of protons and neutrons (or nucleons) together: protons + neutrons = mass number. Since the number of neutrons in the nucleus varies, you can have different amounts of neutrons in the same type of atom. These varied types are called isotopes.
Hope this helps.
Complete question
The complete question is shown on the first and second uploaded image
Answer:∈
Answer to first question is shown on the second uploaded image.
Part B the Answer is:
The ratio
is evaluated to be 49.99
Explanation:
The explanation is shown on the third ,fourth and fifth image.
Groups and periods are two ways of categorizing elements in the periodic table. Periods are horizontal rows (across) the periodic table, while groups are vertical columns (down) the table. Atomic number increases as you move down a group or across a period.
<span>To relate or measure the by the quantity of something, not against the quantity</span>