1) Answer is: C. Their components can be separated by physical processes.
Mixtures can be separeted physically, while compounds cannot.
For example if we have mixture of water and alcohol ethanol, we can separate water and ethanol with distillation (process of heating and cooling). Ethanol and water have different boiling points (physical property).
But if we want to separate water (compound) into oxygen and hydrogen, we must brake bonds between oxygen and hydrogen and that is not physical property.
2) Answer is: the atomic models with two protons (red balls with P).
The atomic number (Z) determines total number of protons and uniquely identifies a chemical element, also the atomic number is equal to the number of electrons in neutral atom.
This element (helium He) has two protons and two electrons, number of neutrons (yellow balls with N) is different.
3) Answer is: A. degree Celsius.
The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI).
The Celsius scale was based on 0°C for the freezing point of water and 100°C for the boiling point of water at 1 atm pressure.
The temperature T in degrees Celsius (°C) is equal to the temperature T in Kelvin (K) minus 273,15: T(°C) = T(K) - 273.15.
