The circuit has two oppositely connected ideal diodes in parallel. What is the current flowing in the circuit (in $A$)?

The energy levels of a certain atom are $A, B,$ and $C$ in increasing order of energy,i.e.,$E_A < E_B < E_C$. If $\lambda_1, \lambda_2,$ and $\lambda_3$ are the wavelengths of radiation corresponding to transitions $C \to B, B \to A,$ and $C \to A$ respectively,which of the following relations is correct?

The area (in sq units) of the quadrilateral formed by two pairs of lines $\lambda^2 x^2 - m^2 y^2 - n(\lambda x + m y) = 0$ and $\lambda^2 x^2 - m^2 y^2 + n(\lambda x + m y) = 0$ is:

The speed of sound in oxygen $(O_2)$ at a certain temperature is $460 \; m/s$. The speed of sound in helium $(He)$ at the same temperature will be (assume both gases to be ideal): (in $; m/s$)

Cardiac muscles contract:

Which pair of substances gives the same gaseous product when they react with water?