Which of the following is not a reason why actual yield is less than theoretical yield?
loss of product during purification
presence of impure reactants
competing side reactions
conservation of mass

Icant see the pictures 

500bc indiais the answer.

What are the statements?

Van der waals forces are temporary electromagnetic forces established between uncharged atoms. some neutral molecules, when close together, can become temporarily “charged,” as electrons move around the atom. water is a polar molecule, the side of the molecule that the hydrogens bond to being more positive, and the opposite side bound to the lone pairs of electrons being more negative. this means that it participates in dipole-dipole interaction (non-polar exhibits dispersion forces), and it has the capacity for hydrogen bonding.