What are the similarities about the mass in amu of 1 atom of carbon and the mass in g of 1 mole of carbon atoms ?

Answer is: value (number) is the same, units are different.

1) One carbon atom has mass of 12 amu (unified atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (proton or neutron).

2) One mole of carbon atoms has mass of 12 g/mol. The mole is the unit (with the unit symbol: mol) of measurement for amount of substance. One mole of carbon atoms has 6.022·10²³ carbon atoms.

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.

they are all solids.