In the NiTi system, there are a number of invariant transformations and solid state phases. How many degrees of freedom are there in the two phase regions and at the invariant points?

we have zero degree of freedom (F = 0) at the first phase region and one degree of freedom (F = 1) at the second phase region

Explanation:

given the diagram;

C = 2 { Ti and Ni}, N = 1 {Pr is constant}, P = 3 { L and B}

For degree of freedom,

Gibbs phase rule is applied for invariant point (ex.A)

P + F = C + N

3 + F = 2 + 1

F = 3 - 3

F = 0

For the second phase region ( ex.B)

C = 2, N = 1, P = 2

P + F = C + N

2 + F = 2 + 1

F = 3 - 2

F = 1

Therefore we have zero degrees of freedom (F = 0) at the first phase region and one degrees of freedom (F = 1) at the second phase region

explanation:  

an electrode is a metal whose surface serves as the location where oxidation-reduction equilibrium is established between the metal and what is in the solution.