Widal test is used for the diagnosis of

Two blocks are connected by a spring. The combination is suspended,at rest,from a string attached to the ceiling,as shown in the figure. The string breaks suddenly. Immediately after the string breaks,what is the initial downward acceleration of the upper block of mass $2\,m$?

In the circuit shown in the figure,the power developed across the $1 \Omega$,$2 \Omega$,and $3 \Omega$ resistors are in the ratio of:

If the sum of two of the roots of $x^3+p x^2-q x+r=0$ is zero,then $p q$ is equal to

Which of the following oxides reacts with both $HCl$ and $NaOH$?

Which of the following is used as an antibiotic?