If $\vec{a} = 2\hat{i} + \lambda \hat{j} + \hat{k}$ and $\vec{b} = \hat{i} + 2\hat{j} + 3\hat{k}$ are orthogonal, then the value of $\lambda$ is

Question

If $\vec{a} = 2\hat{i} + \lambda \hat{j} + \hat{k}$ and $\vec{b} = \hat{i} + 2\hat{j} + 3\hat{k}$ are orthogonal, then the value of $\lambda$ is –

$\frac{3}{2}$

$-\frac{5}{2}$

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