Answer:
9) 60; 10) 0.2583
Explanation:
9) M(SiO₂)=28+16*2=60 (gr/mol);
10) if one mole is in 60gr., then for 15.5 gr.:
1/60=x/15.5; ⇒ x=15.5/60≈0.2583(mol).
