Select the correct statement from the following regarding cell membrane.

Lipids are arranged in a bilayer with polar heads towards the inner part.

Fluid mosaic model of cell membrane was proposed by Singer and Nicolson.

$\displaystyle \mathrm{Na}+$ and $\displaystyle \mathrm{K}^{+}$ ions move across cell membrane by passive transport.

Proteins make up $\displaystyle 60$ to $\displaystyle 70$% of the cell membrane.