Q. The work function ( $\phi$ ) of some metals is listed below. The number of metals which will show photoelectric effect when light of 300 nm wavelength falls on the metals is :

Metakl Li N K Mg Cu Ag Fe Pt W

$\phi( eV )$ 2.4 2.3 2.2 3.7 4.8 4.3 4.7 6.3 4.75

NTA AbhyasNTA Abhyas 2022 Report Error

A

2

B

4

C

6

D

8

Solution:

Energy of photon $=\frac{\text{h} \text{c}}{\lambda }\text{J}=\frac{\text{h} \text{c}}{\text{e} \lambda }\text{e}\text{V}$
$=\frac{6.625 \times 10^{- 34} \times 3 \times 10^{8}}{300 \times 10^{- 9} \times 1.602 \times 10^{- 19}}=4.14 \, \text{e}\text{V}$
For photoelectric effect to occur, energy of incident photons, must be greater than work functions of metal. Hence, only Li, Na, K and Mg have work functions less than 4.14 eV.

Questions from NTA Abhyas 2022

1. An alkene $\left(\right.A\left.\right)$ on ozonolysis gives a mixture of two carbonyl compounds. Mixture on Clemmensen reduction gives just one alkane $\left(\right.B\left.\right)$ . $\left(\right.B\left.\right)$ is the lowest alkane which in pure form can not be prepared by standard Wurtz method. $\left(\right.A\left.\right)$ is

2. A cation is in the centre touches three anions. Assume that the anions also touch each other. The limiting radius ratio, $r^{+}/r^{-}$ is

3. Blue colour of alkali and alkaline earth metals in liquid $NH_{3}$ is due to

4. Which of the following oxides is strongly basic?

5. In a $10litre$ box $2.5mole$ hydroiodic acid is taken. After equilibrium $2HI\rightleftharpoonsH_{2}+I_{2}$ the concentration of $HI$ is found to be $0.1 \, \text{mol} \, \text{L}^{- 1}$ . The concentration of $\left[H_{2}\right]$ at equilibrium in $molL^{- 1}$ , is

Chemistry Most Viewed Questions

1. If for a certain reaction $\Delta_{r}H$ is $30\, kJ\, mol^{-1}$ at $450 \,K$, the value of $\Delta_{r}S$ (in $JK^{-1}\, mol^{-1})$ for which the same reaction will be spontaneous at the same temperature is

NEET 2020

2. If $8\,g$ of a non-electrolyte solute is dissolved in $114\, g$ of n-octane to reduce its vapour pressure to $80\%$, the molar mass (in $g \,mol^{-1})$ of the solute is [Given that molar mass of n-octane is $114 \,g\, mol^{-1}]$

NEET 2020 Solutions

3. An organic compound contains $78 \%$ (by wt.) carbon and remaining percentage of hydrogen. The right option for the empirical formula of this compound is: [Atomic wt. of $C$ is $12, H$ is $1$]

NEET 2021 Some Basic Concepts of Chemistry

4. At standard conditions, if the change in the enthalpy for the following reaction is $-109 \,kJ\, mol^{-1}$ $H_{2(g)}+Br_{2(g)} \to 2HBr_{(g)}$ Given that bond energy of $H_{2}$ and $Br_{2}$ is $435\,KJ\,mol^{-1}$ and $192\,KJ\,mol^{-1}$ , respectively, what is the bond energy (in $KJ \,mol^{-1})$ of $HBr$ ?

NEET 2020

5. The density of 2 M aqueous solution of NaOH is 1.28 g/cm$^3$. The molality of the solution is
[Given that molecular mass of NaOH = 40 g mol$^{-1}$]

NEET 2019 Some Basic Concepts of Chemistry

Latest Updates