Which of the following is the most stable?

Which one of the following does not correctly represent the order of property indicated against it?

If $y_k$ is the $k$-th derivative of $y$ with respect to $x$,and $y = \cos(\sin x)$,then $y_1 \sin x + y_2 \cos x$ is equal to

Assertion $(A)$ The effective resistance of the network between $P$ and $Q$ is $\frac{4}{5} r.$

Reason $(R):$ Symmetry can be applied to be network with respect to centre.

The value of $a$ for which the system of equations $a^3x + (a + 1)^3y + (a + 2)^3z = 0$,$ax + (a + 1)y + (a + 2)z = 0$,$x + y + z = 0$ has a non-zero solution is

The angle between the lines whose direction cosines satisfy the equations $l+m+n=0$ and $l^2+m^2-n^2=0$ is