Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

There are two bags each of which contains n balls. A man has to select an equal number of balls from both the bags. Prove that the number of ways in which a man can choose at least one ball from each bag is^(2n)C_n-1.

RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C_(4) plants?

The Tamil Nadu Government has banned the use of one-time use throw away plastics.Why do you think this is important?

Read the following paragraph and answer the questions given below: In the Modem Periodic table, the elements are arranged in the increasing order of their atomic numbers . Thi s arrangement is based on the Modern Periodic law, which states that the properties of elements are a periodic function of their atomic numbers. In the Modern Peroidic table, each column is called a group and each row is called a period. Elements within the same group show similarity and ggradation in properties. This is due to the same number of electrons in the outermost shell. Which pair of elements do you think will have similar properties? (a) Sodium and Argon (b) Sodium and Potassium (c) Potassium and Neon

Water is a universal slvent. But alcohol also dissolves most of the substances soluble in water and also many more. Boiling point of water is 100^(@)C and that of alcohol is 80^(@)C. The specific heat of water is much higher than the specific heat of alcohol. (a) List out three possible differences if instead of water as teh liquid in our body we had alcohol. (b) What value can you derive from this special property of water and its innumerable uses in sustaining life on earth ?

Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying on it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts on it is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object and a buoyant force also acts on the object. Thus, true free fall is possible only in vacuum. For a freely falling object, the velocity on reaching the earth and the time taken for it can be calculated by using Newton's equations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite to the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. Which force acts on the stone in free fall after you release it?

Take two eggs and drop them from a certain height one by one . Drop one egg onto a concrete floor and another one onto a cushion pillow . What changes do you notice ? When the egg is dropped onto a concrete floor , it breaks. But , the egg is dropped onto the cushion pillow . What changes do you notice ? When the egg is dropped onto a concrete floor , it breaks . But , the egg dropped onto the cushion pillow does not break . Can you explain why ?

Lift an object up from the ground. Work done by the force exerted by you on the object moves it in upward direction. Thus the force applied is in the direction of displacement. However there exists a force of gravitation on the object at the same time • Which one of these forces is doing positive work? • Which one is doing negative work? • Give reasons

Read the following passage and answer the questions that follow Rahini and her parents were watching at a television An advertisement mashed on the screen which was promoting use of sanitary napkins. Rahini's parents suddenly changed the channel, but she objected to her parents and explained the need and importance of such advertisement. (a) What is first menstruation called? When does it occur? (b) List out the napkin hygiene measures taken during menstruation? (c) Do you think that Rahini's objection towards her parents was correct? If so, why?