9. any hermitian 2 x 2 matrixh can be expressed in terms of the 2 x 2 identity matrix i and three pauli sigma matrices oo , as h = a,i+2 a,, where j=x,y.z (a) a

9. Any Hermitian 2 x 2 matrixH can be expressed in terms of the 2 x 2 identity matrix I and three Pauli sigma matrices OO , as H = a,I+2 a,, where j=x,y.z (A) a, is real and a, a, a, are pure imaginary (6) 4 4 a, a, are al pure imaginary (C) a, is pure imaginary and a, a, a, are all real (D) a,. 3, a, a, are all real