If the coefficient of x in

(a) 3

The coefficient of $x$ in the given expansion where $x$ occurs at the $(r+1)$ th term.

We have:

${ }^{5} C_{r}\left(x^{2}\right)^{5-r}\left(\frac{\lambda}{x}\right)^{r}$

$={ }^{5} C_{r} \lambda^{r} x^{10-2 r-r}$

For it to contain $x$, we must have :

$10-3 r=1$

$\Rightarrow r=3$

$\therefore$ Coefficient of $x$ in the given expansion:

${ }^{5} C_{3} \lambda^{3}=10 \lambda^{3}$

Now, we have

$10 \lambda^{3}=270$

$\Rightarrow \lambda^{3}=27$

$\Rightarrow \lambda=3$