1. (a) Write the molecular formula of the following carbon compounds :
(i) Methane
(ii) Propane
(b) Carbon compounds have low melting and boiling points. Why?
explanation: a) molecular formula of methane is CH4 and propane is CH3CH2CH3
b) carbon compounds have the weaker intermolecular force of interactions hence they have lower boiling and melting points
2. The electrons in the atoms of two elements X and Y are distributed in
three shells having 1 and 7 electrons respectively in their outermost
shells.
(a) Write the group numbers of these elements in the Modern Periodic
Table.
(b) Write the molecular formula of the compound formed when X and
Y combine with each other.
(c) Which of the two is electropositive?
explanation: a) element X has 1 electron in the outermost shell hence it belongs to group 1. while element Y has 7 electrons in the outermost shell to become noble gas and complete its octet it requires only one electron hence it belongs to group 17.
b) x which belongs to group 1 has 1 electron in the outermost shells. and Y belongs to group 17 have 7 electrons in the outer shell. to make a stable compound X and Y will share their electron. and forms compound XY.
c) if an element has a tendency to donate electrons then it is electropositive while an element that accepts electrons is electropositive. so, element X is electropositive and element Y is electronegative.
3. (a) Which of the following flowers will have a higher possibility of
self-pollination?
Mustard, Papaya, Watermelon, Hibiscus
(b) List the two reproductive parts of a bisexual flower.
explanation: a) out of all the flowers mustard is bisexual and hence has the ability to self-pollinate.
b) the reproductive parts of bisexual contain gem cells:
1. anthers (male reproductive organ)
2. ovary (female reproductive organ)
the function of the ovary is to produce ovules and the function of the anthers is to store pollens hence after fertilization ovary transforms into fruits and the ovule transforms into seeds.
4. Which one of the two multicellular organisms Spirogyra and Planaria
reproduces by regeneration and why? Give an example of any other
organism which can also reproduce by the same process.
explanation: a) planaria reproduce by binary fission. the formed head and tail regenerated into the whole organism. while spirogyra reproduces by spore formation as asexual reproduction and by conjugation sexually.
b) hydra also reproduces by regeneration.
5.(a) What is variation? List two main reasons that may lead to variation in a population.
OR
(b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the F1 progeny.
(ii) If the plants of F1 progeny are self-pollinated, then what would be observed in the plants of F2 progeny?
(iii) If 100 plants are produced in F2 progeny, then how many plants will show the recessive trait?
explanation: a) variation refers to differences between two individuals or populations. the mutation is the ultimate source of variation.
sources of variation:
1. mutation
2. gene flow
3. geographic isolation
4. reproductive isolation
5. sexual reproduction
iii) the phenotypic ratio of the cross is 3:1
the total number of organisms is 100.
the recessive trait showed by (1/4)*100
= 25
6. (a) (i) Name and state the rule to determine the direction of force experienced by a current-carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
(ii) An alpha particle while passing through a magnetic field gets projected north. In which direction will an electron project when it passes through the same magnetic field?
OR
(b) (i) What is a solenoid?
(ii) Draw the pattern of magnetic field lines of the magnetic field produced by a solenoid through which a steady current flows.
explanation: i) the Flemings Left Hand Rule is used to determine the direction of force A current-carrying conductor when placed in a magnetic field will experience a force by this conductor. The direction of force acting on this conductor will depend upon the direction of the magnetic field and the current flowing through the conductor.
ii) A positively charged particle (alpha-particle) projected towards the west is deflected towards the north by a magnetic field. The direction of the magnetic field is Upward.
OR
b)i) a cylindrical coil of wire acting as a magnet when carrying electric current. it is used as an electromagnet.
ii)
7. (a) What is ozone? How is it formed in the upper layers of the atmosphere? How does ozone affect our ecosystem?
OR
(b) (i) List two human-made ecosystems.
(ii) we don't need to clean a pond in the same manner as we do in an aquarium. give a reason to justify this statement.
explanation: Ultraviolet radiations split the oxygen molecules present in the stratosphere into free oxygen atoms. These free oxygen atoms then combine with molecular oxygen to form ozone.
O2 → O + O
O2 + O → O3
The ozone layer is a protective layer which protects the earth from harmful UV radiation. Any damage to the ozone layer would result in UV rays entering the earth's atmosphere. These UV rays can cause diseases such as skin cancer and cataract. They can also adversely affect the crops. The ozone layer is damaged as a result of chlorofluorocarbons. These are often used in refrigerators, air conditioners and fire extinguishers.
OR
b) i) two human-made ecosystem is a pond and a garden.
ii) A pond or lake is a natural ecosystem. They are self-sustaining and complete, in then, all the organisms of the food chain are available. If any organism dies, there are decomposers to decompose their bodies into simpler substances.
An aquarium, on the contrary, is an artificial and incomplete ecosystem. The abiotic components are not supplied naturally to it. It may not have all the biotic components in it. If a fish dies in an aquarium in the absence of a decomposer, it will lie there like a rotten body, polluting the water of the aquarium. Hence, we need to clean it.
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