1. In science, a measurement is collection of quantitative or numerical data that describes a property of an object or event. A measurement is made by comparing a quantity with a standard unit. Since this comparison cannot be perfect, measurements inherently include error, which is how much a measured value deviates from the true value. The study of measurement is called metrology. There are many measurement systems that have been used throughout history and across the world, but progress has been made since the 18th century in setting an international standard. The modern International System of Units (SI) bases all types of physical measurements on seven base units. International System of Units (SI) is an official system of measurement used throughout the world for units in length, volume, mass, temperature, and time.
2. Protons and neutrons can be very similar especially with their masses, this could be explained by using the atomic mass unit which is the unit commonly used to express the masses of protons, neutrons, and nuclei. Protons and electrons have electrical charges, they equal in magnitude but have opposite signs. Unlike protons and electrons, neutrons have no charge at all. When a proton and neutron are paired together the charges are canceled