Which one of the following is not a functional unit of an ecosystem?

The pairs of straight lines $x^2-3xy+2y^2=0$ and $x^2-3xy+2y^2+x-2=0$ form a

The diameter of the objective lens of a telescope is $250 \ cm$. For light of wavelength $600 \ nm$ coming from a distant object,the limit of resolution of the telescope is close to:

If $\int_{-1}^{4} f(x) \, dx = 4$ and $\int_{2}^{4} (3 - f(x)) \, dx = 7$,then the value of $\int_{2}^{-1} f(x) \, dx$ is

If $\overrightarrow{a}=\hat{i}+\hat{j}+\hat{k}$,$\overrightarrow{b}=\hat{i}+\hat{j}$,$\overrightarrow{c}=\hat{i}$ and $(\overrightarrow{a} \times \overrightarrow{b}) \times \overrightarrow{c}=\lambda \overrightarrow{a}+\mu \overrightarrow{b}$,then $\lambda+\mu$ is equal to:

$A$ body of $5\, kg$ weight kept on a rough inclined plane of angle $30^\circ$ starts sliding with a constant velocity. Then the coefficient of friction is: