Which of the following halides has the maximum melting point?

If the altitudes of a triangle are in arithmetic progression,then the sides of the triangle are in

In the circuit shown in the figure below, which of the following statements is incorrect?

If $\left|\begin{array}{ccc}\cos (A+B) & -\sin (A+B) & \cos 2 B \\ \sin A & \cos A & \sin B \\ -\cos A & \sin A & \cos B\end{array}\right|=0$,then $B$ is equal to

If the distance between the points $(a \cos \theta, a \sin \theta)$ and $(a \cos \phi, a \sin \phi)$ is $2a$,then $\theta$ is equal to

What does orthoboric acid contain?