Which of the following conditions remain constant in Boyle's law?

Volume and pressure
Density and temperature
Pressure and number of moles
Temperature and number of moles

Temperature and number of moles are the conditions which remain constant in Boyle's law.

Explanation:

Boyle's law states that at constant temperature the pressure of a gas is inversely proportional to the volume of gas.

Mathematically, it is represented as follows.

As equation for ideal gas is as follows.

PV = nRT

And, at constant temperature the pressure is inversely proportional to volume which also means that number of moles are also constant in Boyle's law.

Thus, we can conclude that temperature and number of moles are the conditions which remain constant in Boyle's law.

solute : a solute is a substance that is dissolved in another substance is known as a solvent. it is mixed with a special mixture know as homogeneous mixture.

solvent: a solvent is a substance that dissolved a solute, which results in a solution is known as solvent.

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.