Which of the following is a Lewis acid?

Liquids $A$ and $B$ form an ideal solution. If $X_A$ and $Y_A$ are the mole fractions of $A$ in the solution and in vapour phase in equilibrium,respectively,then (Given $P_A^o > P_B^o$):

Two fair dice are rolled. The probability of the sum of digits on their faces being greater than or equal to $10$ is

The biquadratic equation,two of whose roots are $1+i$ and $1-\sqrt{2}$,is

Which relation is correct for an isochoric process?

The maximum velocity of electrons emitted from a metal surface is $V$ when the frequency of light falling on it is $f$. What is the maximum velocity when the frequency becomes $4f$?