13.14 Given below are densities of some solids and liquids. Give rough estimates of the size of their atoms:

Substance	Atomic Mass (u)	Density ( ${10}^3\mathit{K}\mathit{g}{\mathit{m}}^{-3})$
Carbon ( Diamond)	12.01	2.22
Gold	197.00	19.32
Nitrogen (liquid)	14.01	1.00
Lithium	6.94	0.53
Fluorine (liquid)	19.00	1.14

[Hint : Assume the atoms to be 'tightly packed' in a solid or liquid phase, and use the known value of Avogadro's number. You should, however, not take the actual numbers you obtain for various atomic sizes too literally. Because of the crudeness of the tight packing approximation, the results only indicate that atomic sizes are in the range of a few Å].

A capillary glass tube records a rise of 20 cm when dipped in water. When the area of cross- section of the tube is reduced to half of the former value, water will rise to a height of:-

The root mean square speed of molecules of a gas is 1260 m/s. The average speed of the gas molecules is

A block rests on an inclined plane making an angle of 30° with the horizontal. The coefficient of static friction between block and the plane is 0.8. If the frictional force on the block is 10 N, then mass of block (in kg) (Take g = 10 m/s² )

In a container, 1 g of hydrogen and 1 g of oxygen are taken. Find the ratio of hydrogen pressure to oxygen pressure,

Find the temperature of H₂ gas at which its rms speed is equal to that of O₂ at 47°C.