How do you find the mass number of an element

Explanation:

The mass number is a specific property of the atoms, defined as the sum of the protons and neutrons, which are the subatomic particles that are in the nucleus of the atom.

The electrons do not count for the mass of atoms because their mass is about 1/1840 the mass of a proton or a neutron.

The relative masses of protons and neutrons is 1: 1, then they count equally.

As an example, the mass number of the atom carbon-12 is calculated in this way:

The number 12 added to the name in carbon-12, stands for its mass number.

Also, the mass number is indicated as a superscript to the left of the chemical symbol of the element, and the atomic number as a subscript to the left of the chemical symbol. For the example of carbon-12 that is:

Percent yield of hydrogen is 87.096%

Explanation:

Theoretical yield = 155g

Experimental yield = 135g

% yield = [experimental yield / theoretical yield] * 100

% yield = (135 / 155) * 100

% yield = 0.87096 * 100

% yield = 87.096 %

The percentage yield of hydrogen is 87.096%