An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. Name the element.​

Thus, we can say that the element is calcium. This can be clearly understood as ionic compounds have high melting and boiling points in general such as calcium oxide.

The element is Calcium I guess.

Explanation:

Cause calcium oxide has high melting point and is soluble in water.

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.  

they are all solids.