Nitrobenzene gives $N$-phenylhydroxylamine by

In a book of $500$ pages,it is found that there are $250$ typing errors. Assume that Poisson law holds for the number of errors per page. Then,the probability that a random sample of $2$ pages will contain no error,is :

Which of the following reactions can produce aniline as the main product?

$\int_2^3 \frac{dx}{x^2-x}$ is equal to

$A$ radioactive material decays by simultaneous emission of two particles with respective half-lives $1620 \, years$ and $810 \, years$. The time (in years) after which one-fourth of the material remains is:

Two waves having intensity $I$ and $9I$ produce interference. If the resultant intensity at a point is $7I$,the phase difference between the two waves is.....$^o$