The only taxonomic category that has a real existence is...

The length of a pendulum is measured as $1.01 \ m$ and the time for $30$ oscillations is measured as $1 \ \text{minute} \ 3 \ s$. The error in length is $0.01 \ m$ and the error in time is $3 \ s$. The percentage error in the measurement of acceleration due to gravity is:

Which of the following is not a biofertilizer?

The reading of the ammeter in the circuit shown will be: (in $A$)

If the angles made by a straight line with the coordinate axes are $\alpha, \frac{\pi}{2}-\alpha, \beta$,then $\beta$ is equal to

$A$ metallic ring of radius $r$ and cross-sectional area $A$ is fitted into a wooden circular disc of radius $R$ $(R > r)$. If the Young's modulus of the material of the ring is $Y$,the force with which the metal ring expands is