Why does a new flu shot need to be made each year ?

Which statement explains why the bonds between non metals tend to be covalent? the bonds are found to be nondirectional they have large differences in electronegativity they have small differences in electronegativity they have ions that produce an electrostatic pull

How many moles of oxygen react with 12 moles of aluminum

Find the mass, in grams, of 5.00*10^23 molecules of f2