# Problem: Part D. Which element does X represent in the following expression: 3215X?Enter the chemical symbol of the element. Atoms are composed of three fundamental particles. Protons are positively charged, neutrons are neutral, and electrons are negatively charged. Protons and neutrons are clustered into a dense core called the nucleus, whereas electrons are found outside of the nucleus at a relatively large distance. Elements differ from one another by how many protons their atoms they contain. The number of protons is called the atomic number (Z) of the element. Since protons and neutrons make up most of the mass of an atom, the sum of the protons and neutrons is its mass number (A). In neutral atoms, the numbers of protons and electrons are equal. In ions, the numbers of electrons and protons are not equal.

###### Problem Details

Part D. Which element does X represent in the following expression: 3215X?

Enter the chemical symbol of the element.

Atoms are composed of three fundamental particles. Protons are positively charged, neutrons are neutral, and electrons are negatively charged. Protons and neutrons are clustered into a dense core called the nucleus, whereas electrons are found outside of the nucleus at a relatively large distance. Elements differ from one another by how many protons their atoms they contain. The number of protons is called the atomic number (Z) of the element. Since protons and neutrons make up most of the mass of an atom, the sum of the protons and neutrons is its mass number (A). In neutral atoms, the numbers of protons and electrons are equal. In ions, the numbers of electrons and protons are not equal.