Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
Atomic mass of Helium = 4u
Atomic mass of an atom = no. of protons + no. of neutrons
4 = 2 + no. of neutrons
no. of neutrons = 4 - 2 = 2
Helium has 2 neutrons.
If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom? and (ii) what is the charge on the atom?
With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
For the symbol H,D and T tabulate three sub-atomic particles found in each of them.
Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
Define valency by taking examples of silicon and oxygen.
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 168 X and 188 X in the sample?
Describe Bohr’s model of the atom.
Draw a sketch of Bohr’s model of an atom with three shells.
Write the electronic configuration of any one pair of isotopes and isobars.
Na+ has completely filled K and L shells. Explain.
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
State any two conditions essential for good health.
How is our atmosphere different from the atmospheres on Venus and Mars?
Who discovered cells, and how?
How do annelid animals differ from arthropods?
What is meant by a pure substance?
In the hierarchy of classification, which grouping will have the smallest number of organisms with a maximum of characteristics in common and which will have the largest number of organisms?
Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?
In the following example, try to identify the number of times the velocity of the ball changes: “A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”.
Also identify the agent supplying the force in each case.
Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
Differentiate between homogeneous and heterogeneous mixtures with examples.
What does the odometer of an automobile measure?
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?