If the diameter of a carbon atom is 0.15 nm, the number of carbon atoms that can be placed side by side in a straight line across the length of the scale of length 20 cm long will be:$\mathrm{}$

1.	1.33 × 107	2.	5.46 × 108
3.	1.33 × 109	4.	2.36 × 108

The charge on the oil drop is –1.282 × 10^–18C. The number of electrons present in it would be :

1. 15

2. 8

3. 2

4. 6

An element with a mass number of 81 contains 31.7% more neutrons as compared to protons. The atomic symbol of the element would be :

$1.$ ${}_{35}{}^{81}\mathrm{Br}$
$2.$ ${}_{36}{}^{81}\mathrm{Br}$
$3.$ ${}_{35}{}^{79}\mathrm{Br}$
$4.$ ${}_{36}{}^{79}\mathrm{Br}$

An ion with a mass number of 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. The symbol of the ion is :

$1.$ ${}_{26}{}^{56}\mathrm{Fe}^{+3}$
$2.$ ${}_{26}{}^{57}\mathrm{Fe}^{+3}$
$3.$ ${}_{27}{}^{58}\mathrm{Fe}^{+3}$
$4.$ ${}_{25}{}^{56}\mathrm{Fe}^{+3}$

A nitrogen laser produces radiation at a wavelength of 337.1 nm. If the number of photons emitted per second is 5.6 × 10²⁴,
the power of the laser is:

$\mathrm{}$$1.$ $4.56$ $\times$ ${10}^7$ $\mathrm{J}$
$2.$ $3.33$ $\times$ ${10}^6$ $\mathrm{J}$
$3.$ $1.29$ $\times$ ${10}^6$ $\mathrm{J}$
$4.$ $9.17$ $\times$ ${10}^5$ $\mathrm{J}$

A photon detector receives a total energy of \(3.15 \times 10^{-18}\) J from radiation with a wavelength of 600 nm. How many photons are received by the detector?

$1.$ ${10}^2$
$2.$ $10$
$3.$ $50$
$4.$ $20$

The energy associated with the emission of 2.5 × 10¹⁵ photons in 2 nanoseconds is:
1. \(8 . 28\) \(\times\) \(10^{- 10}\) \(J\)
2. \(8 . 24\) \(\times\) \(10^{11}\) \(J\)
3. \(7 . 12\) \(\times\) \(10^{- 11}\) \(J\)
4. \(2 . 12\) \(\times\) \(10^{-10}\)\(J\)

Emission transitions in the Paschen series end at orbit n = 3 and start from orbit n and can be represented as v = 3.29 × 10¹⁵ (Hz)$\left(\frac{1}{3^2}-\right)$ $\frac{1}{{\mathrm{n}}^2}$. The value of n if the transition is observed at 1285 nm is :

If the velocity of the electron is 1.6 × 10⁶ ${\mathrm{ms}}^{-1}$. The de Broglie wavelength associated with this electron is:  

$1.$ $590$ $\mathrm{pm}$
$2.$ $455$ $\mathrm{pm}$
$3.$ $512$ $\mathrm{pm}$
$4.$ $401$ $\mathrm{pm}$

What is the velocity associated with a neutron that has a wavelength of 800 pm?