Hydrogen bonds are:

a. the sharing of electrons between a hydrogen atom and another atom.
b. the electrostatic interaction between an atom that has lost an electron and an atom that has gained an electron.
c. the interaction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

The answer to your question is: letter C

Explanation:

a. the sharing of electrons between a hydrogen atom and another atom.  This description is not for hydrogen bonding, in hydrogen bonding atoms do not share electrons, to form this bond.

b. the electrostatic interaction between an atom that has lost an electron and an atom that has gained an electron.  This definition is describing an ionic bonding, not a hydrogen bonding.

c. the interaction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. This is the right definition of hydrogen bonding, because is mentioning the interaction between a hydrogen and an electronegative atom.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.