[DaBeef]

18. What is the amount, in moles, of 342.5 g of each of the
following substances?
(a) W(s) (c) SS(s)
(b) NCI3(f) (d) Ca(NO3)2(s)
19. Express the following as molar amounts.
(a) 10.00 g CO2(g) (c) 14.00 g Cr(OH)3(s)
(b) 3.50 g CSH12(g) (d) 6.97 g Al(NO3)3(s)
20. Re-order each of the following groups of substances from lowest
to highest molar mass.
(a) Nb(s), Ti(s), U(s), Sb(s)
(b) F2(g), 12(s), CI2(g), Br2(f)
(c) lr(s), Se(s), GaP(s), HCIO3(s)
(d) NH3(g), SO2(g), K3PO4(s), Pb(s)
21. A student writes down the following information.
mass of beaker = 52.43 g
mass of beaker and CuSO4(s) = 65.41 g
What amount of CUSO4(s), in moles, did the student add to
the beaker?

[Mitch]

Please read forum rules, you need to show your work. We won't do your homework for you, but we'll help.

[AWK]

These are absolutely basic calculations at the very beginning of chemistry learning. Each textbook of chemistry covers this topic. There are hundreds of websites on the internet on the topic, for example:
https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Introductory_Chemistry_(Tro)/08%3A_Quantities_in_Chemical_Reactions/8.4%3A_Making_Molecules%3A_Mole_to_Mass_(or_vice_versa)_and_Mass-to-Mass_Conversions

Moreover there are some important printing errors in your post:

(a) W(s) (c) SS(s)
(b) 3.50 g CSH12(g) (d) 6.97 g Al(NO3)3(s)