a
Direction of polarisation \(=\hat{\mathrm{E}}=\hat{\mathrm{k}}\)

Direction of propagation \(=\hat{\mathrm{E}} \times \hat{\mathrm{B}}=\frac{\hat{\mathrm{i}}+\hat{\mathrm{j}}}{\sqrt{2}}\)

\(\therefore \hat{\mathrm{E}} \times \hat{\mathrm{B}}=\frac{\hat{\mathrm{i}}+\hat{\mathrm{j}}}{\sqrt{2}}\)

\(\hat{\mathrm{B}}=\frac{\hat{\mathrm{i}}-\hat{\mathrm{j}}}{\sqrt{2}}\)