Which of the following has the highest octane number?

$A$ steel meter scale is to be ruled so that millimeter intervals are accurate within about $5 \times 10^{-5} \ m$ at a certain temperature. The maximum temperature variation allowable during the ruling is (Coefficient of linear expansion of steel $= 10 \times 10^{-6} \ K^{-1}$) (in $^{\circ} C$)

The image of the line $x+y-2=0$ in the $y$-axis is

The angle between the lines $2x = 3y = -z$ and $6x = -y = -4z$ is ......... $^o$.

$A$ body is projected vertically from the surface of the earth of radius $R$ with a velocity equal to half of the escape velocity. The maximum height reached by the body is

The packing efficiency of the two-dimensional square unit cell shown below is ........... $\%$