Select the correct statement from the following regarding

1. Na⁺ and K⁺ ions move across cell membrane by passive transport
2. Proteins make up 60 to 70% of the cell membrane.
3. Lipids are arranged in a bilayer with polar heads towards the inner part.
4. Fluid mosaic model of cell membrane was proposed by Singer and Nicolson

Fluid mosaic membrane model was proposed by Singer and Nicholson in 1972. It is most accepted model of structure of biomembrane.