Which of the following statements about the reabsorption process in Henle's loop are correct? (a) The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes. (b) Urine gets concentrated in Henle's loop. (c) Reabsorption of $Na^{+}$ and water takes place in Henle's loop. (d) Active or passive transport of electrolytes occurs in the ascending limb of Henle's loop. Choose the correct answer from the options given below:

An ideal Zener diode with breakdown voltage of -3 V is reverse biased with a negative input voltage $V_{i}=-5$ V. The magnitude of voltage difference between point B and A is: [Image Placeholder]

A point charge Q is placed inside a cavity within a solid isolated conducting sphere. Consider points A, B and C as shown in the figure, where the magnitudes of the electric fields are $E_{A},$ $E_{B}$, $E_{C},$ respectively. The points B and C are at the same distance from the center of the solid sphere. The correct option is : [Image Placeholder]

For sound waves, if the number of nodes for the $5^{th}$ harmonic of an open-ended pipe is n and that for the $9^{th}$ harmonic of the same pipe with one of its ends closed is m, the ratio $\frac{n}{m}$ is

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The first ionization enthalpy of O is lower than that of N and F. Reason R: The loss of an electron from O leads to stable half-filled p orbital. In light of the above statements, choose the most appropriate answer from the options given below: