D = mass / volume
d = 100 g / 100 mL
d = 1.0 g/mL
It is a physical change because you can not put it back like it was
2H2 (g) + O2 (g) -->2H2 O(g)
mole ratio of H2:O2=2:1
7.25/2=3.625
This is a one-step unit analysis problem. Since we are staying in moles, grams of our compound, and thus molar mass, is not needed.
1 mole is equal to 6.022x10²³ particles as given, so:

<h3>
Answer:</h3>
2.49 mol
Let me know if you have any questions.
Answer:
Its quite vague, instead you could say an atom is the smallest building block which further consists of subatomic particles like protons, neutrons and electrons :)
Hope thi helps :) and I'd appreciate if you'd mark brainliest because ive been stuck on the same rank for quite a long time :(