39. Determine the number of moles of compound in each of the following samples. (Hint: See Sample
Problem 1-13).
a. 4.50 g H2O
b. 471.6 g Ba(OH)2
C. 129.68 g Fe3(PO4)2
40. Determine the percentage composition of each
of the following compounds. (Hint: See Sample
Problem 1-14).
b. AgNO3
.c. Mg(OH)2
a. NaCl

Help me please for this two question

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.