Five elements $A, B, C, D$ and $E$ have work functions $1.2 \ eV, 2.4 \ eV, 3.6 \ eV, 4.8 \ eV$ and $6 \ eV$ respectively. If light of wavelength $4000 \ \mathring{A}$ is allowed to fall on these elements,then photoelectrons are emitted by:

When an electric current is passed through acidulated water,$112 \ mL$ of hydrogen gas at $N.T.P.$ is collected at the cathode in $965 \ seconds$. The current passed,in amperes,is:

Which of the following theories provides the latest explanation for the closure of stomata?

The $P-V$ diagram of an ideal gas is as shown in the figure. The work done by the gas in the process $ABCD$ is:

The solubility of barium iodate in an aqueous solution prepared by mixing $200 \ mL$ of $0.010 \ M$ barium nitrate with $100 \ mL$ of $0.10 M$ sodium iodate is $X \times 10^{-6} mol dm ^{-3}$. The value of $X$ is $.....$
Use: Solubility product constant $\left(K_{ sp }\right)$ of barium iodate $=1.58 \times 10^{-9}$

The number of unpaired electrons in an $O_2$ molecule is