The Fundamental Unit of Life — Science STD 9 — Question

How will you separate a mixture of iron filings and powdered carbon?

Why do solids are generally denser than liquids and gases?

In what respects does a true solution differ from a colloidal solution?

Study the data given below and answer the questions which follow

Particle	Electrons	Protons	Neutrons
A	2	3	4
B	10	9	8
C	8	8	8
D	8	8	10

i. Write the mass number and atomic number of particles A, B, C, D.
ii. Which particles represent a pair of isotopes? Explain.

i. What is meant by frequency of sound waves?
ii. Give the range of frequencies of sound waves that an average human ear can detect.
iii. A source of wave produces 20 crests and 20 troughs in 0.2 s. The distance between a crest and next trough is 50 cm. Find the
a. wavelength
b. frequency
c. time period of the wave.

Mention any three human activities which are responsible for depletion of the ozone layer.

List the basis on which Aristotle classified organisms?

Distinguish between the following:
Chromoplast and chloroplast.