English Medium Class 9 - CBSE Question Bank Solutions for Science

What is the difference between the molecule of an element and the molecule of a compound? Give one example of each.

One of the forms of a naturally occurring solid compound P is usually used for making the floors of houses. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. When 50 g of reactant P was heated strongly, than 22 g of a gas Q and 28 g of a solid R were produced as products. Gas Q is the same which produced brisk effervescence on adding dilute HCl to P. Gas Q is said to cause global warming whereas solid R is used for white-washing.

1. What is (i) solid P (ii) gas Q, and (iii) solid R.
2. What is the total mass of Q and R obtained from 50 g of P ?
3. How does the total mass of Q and R formed compare with the mass of P taken ?
4. What conclusion do you get from the comparison of masses of products and reactant ?
5. Which law of chemical combination is illustrated by the example given in this problem ?

Work out the formula for magnesium hydrogencarbonate.

What are (i) ionic compounds, and (ii) molecular compounds ? Give two examples of each type of compounds.

The cation of an element has :

Molecular compounds are usually formed by the combination between :

An element A forms an oxide A2O5.

What is the valency of element A ?

An element X forms the following compounds with hydrogen, carbon and oxygen :

H₂X, CX₂, XO₂, XO₃

State the three valencies of element X which are illustrated by these compounds.

Calculate the mass of 3.011 × 1024 atoms of carbon.

A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following (Fig. 1.1) would correctly represent the result? Justify your choice.

Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.

Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?

It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?

Which of the following contains maximum number of molecules?

Rutherford’s α–particle scattering experiment showed that

1. electrons have negative charge
2. the mass and positive charge of the atom is concentrated in the nucleus
3. neutron exists in the nucleus
4. most of the space in atom is empty Which of the above statements are correct?

In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, ~ 1.00% of the α-particles were found to deflect at angles > 50º. If one mole of α-particles were bombarded on the gold foil, compute the number of α-particles that would deflect at angles less than 500.

Intestine absorb the digested food materials. What type of epithelial cells are responsible for that?

Which is not a function of epidermis?

Fats are stored in human body as