Answer:
I want to say option C: Testing which surfa e is easier to slide a wooden block across.
Explanation:
I'm not 100 % sure though with my answer. I'm truly so very sorry if my answer is wrong. I tried my best.
Answer:
meter the mean free path of hydrogen atoms in interstellar space.Explanation:
The mean free path equation is given as:

Where"
d = diameter of hydrogen atom in meters
n = number of molecules per unit volume
We are given: d = 100 pm = 



meter the mean free path of hydrogen atoms in interstellar space.
Answer:
= 20.82 g of BaCl2
Explanation:
Given,
Volume = 200 mL
Molarity = 0.500 M
Therefore;
Moles = molarity × volume
= 0.2 L × 0.5 M
= 0.1 mole
But; molar mass of BaCl2 is 208.236 g/mole
Therefore; 0.1 mole of BaCl2 will be equivalent to;
= 208.236 g/mol x 0.1 mol
= 20.82 g
Therefore, the mass of BaCl2 in grams required is 20.82 g