Angstrom = 10^-10 m
for nucleus size are used fermi (femtometer 10^-15 m )
Solid to liquid
Liquid to solid
By adding or removing heat energy aka thermal energy
It would be the first option.
Explanation-
The number of protons is equal to the atomic number the number of neutrons is the mass minus the atomic number.
The speed of the snail is given by:

where S is the distance covered by the snail and t the time taken.
The snail in the problem moves by S=18 mm in t=24 s, therefore its speed is
