Answer : The balanced reduction half-reaction is:

Explanation :
Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.
Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.
Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.
The given balanced redox reaction is :

The half oxidation-reduction reactions are:
Oxidation reaction : 
Reduction reaction : 
In order to balance the electrons, we multiply the oxidation reaction by 2 and reduction reaction by 3 and then added both equation, we get the balanced redox reaction.
Oxidation reaction : 
Reduction reaction : 
The balanced redox reaction will be:

Thus, the balanced reduction half-reaction is:

Answer is 0.10 mol.
<em>Explanation;</em>
n = m/M
Where n is number of moles (mol), m is the mass of substance (g) and M is the molar mass of the substance (g/mol).
n = ?
m = 0.40 g
M = 4.0 g/mol
From substitution,
n = 0.40 g /4.0 g/mol
n = 0.10 mol
Hence, the balloon has 0.10 mol of He.
Answer:
k = 2,04x10⁻⁵
Explanation:
The equilibrium of acetic acid (CH₃COOH) in water is:
CH₃COOH ⇄ CH₃COO⁻ + H⁺.
And the equilibrium constant is defined as:
k = [CH₃COO⁻] [H⁺] / [CH₃COOH] <em>(1)</em>
The equiibrium concentration of each specie if the solution of acetic acid is 0,05M is:
[CH₃COOH] = 0,05M - x
[CH₃COO⁻] = x
[H⁺] = x
<em>-Where x is the degree of reaction progress-</em>
As the pH is 3, [H⁺] = 1x10⁻³M. That means x = 1x10⁻³M
Replacing in (1):
k = (1x10⁻³)² / 0,05 - 1x10⁻³
k = 1x10⁻⁶ / 0,049
<em>k = 2,04x10⁻⁵</em>
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I hope it helps!
Answer:
I believe it is B,fluorine to complete the octet rule
Explanation: