It allowed him to realize that the mass of an atom is concentrated at its center because the atoms mostly went through the foil but some were deflected. He also realized that an atom probably wasn't just empty space and scattered electron and it had a positive center.
0.115 M means that 0.115 moles of KBr are contained in a volume of 1000 ml, therefore a volume of 350 ml will have (0.115 × 0.35) = 04025 moles
From the formula of molarity moles = molarity × volume in liters
1 mole of KBr is equivalent to 119 g
Therefore, the mass = 0.04025 × 119 g = 4.79 g
A physical change is when something don't permanently change
