You placed an object into a graduated cylinder. The level of water went from 500 ml to 645ml. The object has a mass of 210 g. What is the density of
your object?

Explanation:

The density of a substance can be found by using the formula

From the question

mass = 210 g

volume = final volume of water - initial volume of water

volume = 645 - 500 = 145 mL

We have

We have the final answer as

Hope this helps you

i believe the answer is a.

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.