Which one of the following compounds gives aspirin on reacting with acetic anhydride in the presence of $H_2SO_4$?

Two bodies of mass $1\,kg$ and $3\,kg$ have position vectors $\hat{i} + 2\hat{j} + \hat{k}$ and $-3\hat{i} - 2\hat{j} + \hat{k}$,respectively. The centre of mass of this system has a position vector:

Which of the following orders is not correct?

$A$ cell of $emf$ $E$ has an internal resistance $r$ and is connected to a rheostat. When the resistance $R$ of the rheostat is changed,which is the correct graph of the potential difference $V$ across it?

The wavelengths of electron waves in two orbits is $3: 5$. The ratio of kinetic energy of electrons will be

Copper sulphate is prepared by blowing a current of air through copper scrap and dilute $H_{2}SO_{4}$. Dilute $HNO_{3}$ is also added: