Why did scientists debate the nature of electromagnetic radiation for more than 200
years?

Explanation:

Scientists debated about the nature of electromagnetic radiation for more than 200 years because they could not distinguish if the radiations were made up of waves or just particles. This debate was between 1600 to the early part of 1900s.

Today, it is widely accepted and known that electromagnetic radiations consists of both waves and particles.

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Calculations using the Einstein model link

Electromagnetic waves link

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.