Which of the following is the most stable conformer of butane?

The $IUPAC$ name for the complex $[Co(NO_2)(NH_3)_5]Cl_2$ is:

The sum of the last eight coefficients in the expansion of $(1 + x)^{15}$ is:

The number of common tangents to the circles $x^2 + y^2 = 4$ and $x^2 + y^2 - 6x - 8y = 24$ is:

An object is attached to the bottom of a light vertical spring and set vibrating. The maximum speed of the object is $15 ~cm/s$ and the period is $628 ~ms$. The amplitude of the motion in $cm$ is:

Apical dominance is caused by