B. The atomic number. This is because the atomic number is the same as the number of protons an element has, and the number of protons defines an element.
Answer:
197mL of 0,506M HCl
Explanation:
The reaction of HCl + BaCO₃ is:
BaCO₃(s) + 2HCl → BaCl₂(aq) + CO₂ + H₂O.
The moles of BaCO₃ in 9,85 g are:
9,85 g of BaCO₃ × 
= <em>0,0499 moles of BaCO₃</em>
As 1 mol of BaCO₃ reacts with two moles of HCl, for a complete reaction of BaCO₃ to dissolve this compound in water you need:
0,0499 moles of BaCO₃ × 
=<em> 0,0998 moles of HCl</em>
If you have a 0,506M HCl, you need to add:
0,0998 moles of HCl× 
= 0,197 L ≡ 197mL
I hope it helps!
All are gases so no visible reaction persay, unless in closed quarters and then massive pressure.
Explanation:
Carbon has 3 isotopes. Carbon-12, Carbon-13, and Carbon-14
All of them have an atomic number of 6, which means all of them have 6 protons (if they had different numbers of protons, they'd be different elements).
Since they all have 6 protons, in their elemental forms, they all have 6 electrons, too.
Carbon-12:
Atomic number: 6
Mass number: 12
protons: 6
electrons: 6
neutrons: 6
Carbon-13:
Atomic number: 6
Mass number: 13
protons: 6
electrons: 6
neutrons: 7
Carbon-14:
Atomic number: 6
Mass number: 14
protons: 6
electrons: 6
neutrons: 8
As the volume of a gas increases <em>at constant temperature</em>, the number of particle impacts per unit area decreases.
There is the same number of impacts, but they are spread over a larger surface area.
Thus, the number of impacts per unit area decreases.
