Exposure means that in this case, the virus has entered your body/system.
Developing an immunity to it means that you can not longer have the virus enter your system
The answer is C
Chemical properties or chemical changes are the ones which include changes that alter the identity of a substance. For example: burning of any substance which is also called combustion. You burn a piece of paper it changes its identity. It was cellulose fibres earlier now it’s ash after burning.
You burn petrol it was mixture of hydrocarbons but when burnt it changes to smoke which is just gases like carbon dioxide or nitrogen oxides. This is a chemical change
Changing of states is a physical change not chemical change. Think of meeting of ice the water molecules which were in solid state after melting become water molecules in the liquid state. Similarly, the evaporation or boiling will change the water molecules in the liquid state to the gaseous state also called its vapor state. These do not change identity it’s just the water molecules always may it be any state, solid, liquid or gaseous. So, boiling point and melting point are physical properties not chemical. The identity remains same during these processes.
Mass and color are not chemical properties. They don’t change identity when you measure them. If you weigh yourself on weight u won’t change into something else.
The density of silver can be calculated by using the following formula:
Here, m is mass and V is volume.
To calculate density, mass of silver needs to be calculated first.
In FCC, the number of Ag atoms in a unit cell will be 4, atomic mass of Ag is 107.87 g/mol and number of atoms in 1 mol are 
atoms, thus, mass can be calculated as follows:
.
Now, volume can be calculated as follows:
First convert pm to cm:
Thus,
Putting the value to calculate volume,
Now, calculate density as follows:
Therefore, density of silver is 
.
