Which of the following ions does not exist in an aqueous solution?

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

Silviculture is the cultivation of which of the following?

Assuming the sun to be a spherical body of radius $R$ at a temperature of $T \ K$,evaluate the total radiant power incident on the earth at a distance $r$ from the sun. (Where $r_0$ is the radius of the earth and $\sigma$ is Stefan's constant.)

The major product of the following reaction is:

In the sequence of sets $(1,2,3), (4,5,6), (7,8,9,10), \ldots$,the sum of elements in the $50^{th}$ set is