An element is a type of substance which is made up of only one type of an atom. Taking the example the hydrogen is made up of 1 proton and 1 electron. If any one look at the atom of hydrogen then he notice that the most of the atoms of hydrogen do not contain any neutrons but few of them contain 1 or 2 neutrons.
These different type of hydrogen is known as isotopes which contains same no. of protons but different no. of neutrons.
If you change the proton which means you change the element but if you change the neutron no. means you change its isotope.
The following answers in the blank could be Sigmund Freud who found the psychoanalysis and Karen Horney who is known to be a psychoanalyst. Both of them has the idea that childhood experiences is necessary and plays the important role in the individual as he or she grows.
