Which of the following statements is incorrect?

Which of the following wiring diagrams could be used to experimentally determine $R$ using Ohm's law? Assume an ideal voltmeter and an ideal ammeter.

$\sqrt{3} \operatorname{cosec} 20^{\circ} - \sec 20^{\circ}$ is equal to

$A$ block can slide on a smooth inclined plane of inclination $\theta$ kept on the floor of a lift. When the lift is descending with an acceleration $a$,the acceleration of the block relative to the incline is:

An alloy of gold and copper crystallizes in a cubic lattice in which the gold atoms occupy the lattice points at the corners of the cube and copper atoms occupy the centers of each of the cube faces. Determine the formula of this compound.

Two wires $A$ and $B$ are of the same material. Their lengths are in the ratio $1:2$ and their diameters are in the ratio $2:1$. When stretched by forces $F_A$ and $F_B$ respectively,they experience an equal increase in their lengths. Then the ratio $F_A/F_B$ is: