Why does the size of atom decreases over the period in table?
Across a period, all the electrons are added to the same valence shell. However, with increase in atomic number, the number of positively charged protons in the nucleus increase . The higher the nuclear charge, the harder it pulls on the electrons. So, as atomic number increases across periodic table, the size decreases because of higher electrostatic force between nucleus and electrons.
What happens to RBCs when kept in pure water?
By diffusion, every paricles in free motion tend to move from their higher concentration to lower concentration. In the same way, by osmosis, water tends to move from higher concentration of free water molecules to their low concentration. The cell membrane in RBCs are semi permeable, which means that the solutes can not pass through them but the water molecules can easily move through them. So, when RBCs are kept in pure water, solutes cannot pass through the membrane but only water. Many water molecules bind to solutes inside the RBCs; so, the concentration of free water molecules is lower inside. In contrast, there is higher concentration of free water molecules outside in pure water. So, water moves inside cell from outside from their higher to lower concentration. Eventually, with too much water going in, the pressure builds up on the cell membrane and it breaks up. So, RBcs lyse open in pure water.
What is Newton's Third Law of Motion?
Newton's Third Law of Motion states that to every action, there is Equal but Opposite reaction. In real life, it means that if exerts a force on B, B exerts the same quantity of force on A, but the force A experiences is in the opposite direction to what force B experienced. It must be noted that both the objects experience force. So, if you slap on somebody's cheek with your hand, the force towards cheek is an action. The cheek hits back towards the hand at equal force; it's a reaction. The law also holds true for pulling forces like in gravitational forces. The earth pulls on an apple with the same force as the apple pulls on the earth. The effect of force is not so clear because of the masses of earth and apple. The same force produces high acceleration on small apple as compared to a huge earth.