2.41 molecules, should be it
<u>Answer:</u> The uncertainty in the velocity of oxygen molecule is 
<u>Explanation:</u>
The diameter of the molecule will be equal to the uncertainty in position.
The equation representing Heisenberg's uncertainty principle follows:

where,
= uncertainty in position = d = 
= uncertainty in momentum = 
m = mass of oxygen molecule = 
h = Planck's constant = 
Putting values in above equation, we get:

Hence, the uncertainty in the velocity of oxygen molecule is 
I suppose you mean to ask why we can't go through obstacles.
Any atom is surrounded by an electronic cloud. When two atoms get close to each other, the electronic clouds repel each other, preventing them from interpenetrating each other. That same phenomenon, on a larger scale, prevents us from going through matter.
Answer:
0.80 seconds (2 significant figures)
Explanation:
The equation of the reaction is given as;
CICH2CH2Cl (g) --> CH2CHCI (g) + HCl(g)
Rate constant (k) = 2.01 s^-1
From the units of the rate constant, this is a first order reaction.
Initial Concentration = 1.34 M
t = ?
Final concentration = 20% of 1.34 = 0.268 M
The integrated rate law for a first order reaction is given as;
ln[A] = ln[A]o - kt
ln(0.268) = ln(1.34) - 2.01(t)
-2.01(t) = - 1.6094
t = 0.8007 ≈ 0.80 seconds (2 significant figures)