Which of the following is true?

(a) [0.5 0.5, 0.5 0.5] is indentity element for some matrix group

(b) [1 0, 0 1] is identity element for all matrices group of order 2
(c) [1 1, 1 1] is identity element for some matrix group

(d) none of these

To solve this, we need to analyze each of the options to see if the given matrices can act as the identity element for any matrix group. The identity element in a matrix group must satisfy the property that, when multiplied by any matrix in the group, it leaves the other matrix unchanged.

### Option (a):
Matrix: \(\begin{bmatrix} 0.5 & 0.5 \\ 0.5 & 0.5 \end{bmatrix}\)

This matrix is not the identity matrix because it does not leave any matrix unchanged under multiplication. The identity matrix must have 1's on the diagonal and 0's elsewhere. This matrix does not fulfill that requirement, so it **cannot** be an identity element.

### Option (b):
Matrix: \(\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}\)

This is the standard 2x2 identity matrix. For any matrix group of 2x2 matrices, multiplying by this matrix leaves any other matrix unchanged. Therefore, this is the **identity element for all matrix groups of order 2**.

Thus, this option is **true**.

### Option (c):
Matrix: \(\begin{bmatrix} 1 & 1 \\ 1 & 1 \end{bmatrix}\)

This matrix is not the identity matrix because when multiplied by another matrix, it will not leave the other matrix unchanged. Hence, this matrix cannot serve as the identity element for any matrix group.

### Option (d):
This option states that none of the matrices can be the identity element. However, as we've shown, option (b) is true, so this option is **false**.

### Conclusion:
The correct answer is **(b) [1 0, 0 1] is the identity element for all matrix groups of order 2**.

Would you like any further explanation or details?

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Here are five related questions for deeper understanding:

1. What are the properties of an identity matrix in any group of matrices?
2. Can a matrix with all equal non-zero elements ever be an identity matrix?
3. How do we determine if a given matrix is part of a matrix group?
4. What happens when a non-identity matrix is multiplied by an identity matrix?
5. What are the criteria for a matrix group to exist?

**Tip:** The identity matrix is unique for a given size, and it always has 1's on the diagonal and 0's elsewhere.

Which of the following is true?

(a) [0.5 0.5, 0.5 0.5] is identity element for some matrix group

(b) [1 0, 0 1] is identity element for all matrices group of order 2

(c) [1 1, 1 1] is identity element for some matrix group

(d) none of these

Explore which of the given matrices can act as an identity element in a matrix group. The problem focuses on the identity matrix for a matrix group of order 2 and includes an in-depth analysis of matrix multiplication. Suitable for high school students in Grades 10-12.

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