What is the science that deals with the study of plants from various perspectives called?

$A$ 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

Which one of the following elements reduces $NaOH$ to $Na$?

The centre of mass of a system of particles does not depend on:

$A$ horizontal force of $10\,N$ is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and wall is $0.2$. The weight of the block is ........ $N$.

$A$ meter bridge is set up as shown,to determine an unknown resistance '$X$' using a standard $10 \, \Omega$ resistor. The galvanometer shows a null point when the tapping-key is at the $52 \, cm$ mark. The end corrections are $1 \, cm$ and $2 \, cm$ respectively for the ends $A$ and $B$. The determined value of '$X$' is $.......... \Omega$.