Question

protons: (red circle), neutrons: (gray circle), electrons: (dotted circles). left: bohr model with nucleus (1 red, 1 gray) and two dotted electron shells. right: periodic table tile with 2 (top), h (center), 1 (bottom red), hydrogen (bottom red), and a 0 in a box with up/down arrows.

Explanation:

Step1: Determine the number of protons

The atomic number (the red number at the bottom left of the element symbol) is 1, so the number of protons is 1 (since atomic number = number of protons).

Step2: Determine the number of neutrons

The mass number (the black number at the top left) is 2. The formula for mass number is \( \text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons} \). Rearranging for neutrons: \( \text{Number of Neutrons} = \text{Mass Number} - \text{Number of Protons} \). Substituting the values: \( 2 - 1 = 1 \), so there is 1 neutron.

Step3: Determine the number of electrons

In a neutral atom, the number of electrons is equal to the number of protons. Since the number of protons is 1, the number of electrons should be 1. Now, looking at the electron shells: the first shell (closest to the nucleus) can hold a maximum of 2 electrons, but for hydrogen (and in this case, the isotope shown), with 1 proton, the neutral atom has 1 electron. Wait, but the diagram has two electron shells? Wait, no, maybe it's a mistake in the diagram or maybe it's a different representation. Wait, no, let's re - check. Wait, the atomic number is 1, so the number of electrons in a neutral atom is 1. But the diagram shows two dashed circles (electron shells). Wait, maybe it's a mis - drawing, but according to the atomic structure rules, for a neutral hydrogen atom (or its isotope deuterium, which has 1 proton, 1 neutron, and 1 electron), the number of electrons is 1. Wait, but let's go back. The key here is: in a neutral atom, electrons = protons. Protons are 1, so electrons should be 1. But the diagram has two electron shells? Maybe it's a error, but based on the atomic number (1), the number of electrons is 1. Wait, but maybe the question is to find the number of electrons? Let's assume the question is to find the number of electrons. So since protons = 1 (atomic number), electrons = 1 (neutral atom).

Answer:

The number of electrons is 1. (If the question was different, for example, number of neutrons: 1, protons: 1. But based on the diagram and the element (hydrogen, atomic number 1, mass number 2), the number of electrons in a neutral atom is 1.)