Question 1 :
Helium atom has 2 electrons in its valence shell but its valency is not 2. Why?

Question 3 :
If the velocity of a ball is tripled, what will be the ratio of its initial momentum and final momentum?

Question 4 :
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. Why do they get tired while holding it?

Question 5 :
Mention whether jumping of a frog is on the basis of voluntary or involuntary muscles.

Question 6 :
Is drawing a wire of iron metal a physical change or not?

Question 7 :
Mention whether movement of chocolate in your intestine is on the basis of voluntary or involuntary muscles.

Question 8 :
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. How much work do they do in just holding it?

Question 10 :
During an experiment the students were asked to prepare a 10% solution of sugar in water. Ramesh dissolved 10g of sugar in 100g of water while Sarika prepared it by dissolving 10g of sugar in water to make 100g of the solution. Are the two solutions of the same concentration?

Question 11 :
If the velocity of a ball is tripled, what will be the ratio of its initial kinetic energy and final kinetic energy?

Question 15 :
<img style='object-fit:contain' src='https://teachmint.storage.googleapis.com/question_assets/cbse_ncert/61b1d29ef59b460d7261f5f0.JPG' /> In the above figure, a group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the sample taken in a beaker/glass tumbler as shown in the figure. They were amazed to see that milk taken in the glass was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it. They tried the same activity by taking a salt solution but found that light simply passed through it. Name the phenomenon involved in the illumination of milk sample.

Question 18 :
Is bending of an iron rod a physical change or not?

Question 19 :
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. How much work the men do in lifting the box?

Question 22 :
Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identity the correct set of conditions.

Question 23 :
According to the third law of motion, action and reaction _________.