Pre Boards Question Paper 2022

Ans. 1

a. X - Diamond, Y - Graphite, Z - Buckminsterfullerene 

b. X Y and Z substances have C as its constituent element.

Ans.2

a. B loses one electron to become stable

b. C has more bigger radius than A.

Ans.3. 

a. Only after pollination, when pollen has landed on the stigma of a suitable flower of the same species, can a chain of events happen that ends in the making of seeds. 

A pollen grain on the stigma grows a tiny tube, all the way down the style to the ovary. This pollen tube carries a male gamete to meet a female gamete in an ovule. Once the pollen moves down the style, it reaches the ovules, that require sperm to fertilize them and produce new embryos.

b. Ovary grows rapidly and ripens to form a fruit whereas ovule develops tough coat and gradually converted into seed.

The part of seed has two parts

1. Plumule which is the future shoot and 

2. Radical which is the future root.

Ovary and Radicle

Ans.4.

a. Rhizopus (bread  mould)

b. Hypha and Sporangium

Ans.5. The Law of independent assortment states that if the inheritance of more than one character is studied simultaneously, the factors or genes for each character assort out independently to the other gene or factor. The dihybrid cross of Mendel is a good example of independent assortment. The presence of new combinations suggests that the genes are assorted independently.

or

Trait B is likely to have arisen earlier. In asexual reproduction, cell divisions results in creation of similar cells with identical copies of DNA. Therefore, in such species, a trait may come into existence in some members due to sudden mutation induced by the environmental factors. This newly induced trait in some members of species is then inherited by future generations of such organism on replication over a period of time. So, it is but natural for trait B to exist earlier than trait A, as 60 % of population with trait B is likely to have been replicating that trait for a longer period than 10 % of population with trait A.

Ans.6. 

a. upwards

b. (b) Because BC is in the same direction as the direction of field lines. Force is minimum when the direction of current in the conductor is the same as that of the magnetic field. BC will not contribute as the force on this part of the coil will be cancelled by the force on DA.

OR

a. concentric circles represent the magnetic field generated due to flow of current in the wire

b. If the direction of the current in the circuit is reversed then the direction of the magnetic field would also be reversed.

Ans. 7

a. Cause of concern: Ozone layer present in the stratosphere has thinned out by about 18 % over the equator and more so over the Antartica where a big ozone hole appears every year. This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing increased number of skin cancers,cataracts and reduced immunity in human beings. There is increased incidence of blinding of animals ,death of young ones, reduced photosynthesis, higher number of mutations an damage to arteries.

b. Steps to limit damage:

(i) Dispose of pre-1995 refrigerators, freezers, and air conditioning units properly.

(ii) Ban on production and use of chloroflurocarbons.

OR 

a. Biodegradable and non-biodegradable wastes should be discarded in two separate bins as this helps in effective treatment and disposal of these wastes. Biodegradable wastes can be easily disposed by natural way of compositing while non-biodegradable wastes can be sent for safe disposal or recycling. This helps in protecting the environment from pollution. 

b. An improper disposal of wastes means addition of pollutants into the environment- air,water and soil.They will harm living beings,human assets and human beings.Foe example,passage of sewage into water bodies will cause entrophication,stink,development of sludge,killing of animals and source of water borne pathogens.

Ans. 8

a. 19K (Potassium) has 1 electron in the outermost shell. Its electronic confiiguration is 2,8,8,1.

b. 4Be (Beryllium) and 20Ca (Calcium) belong to group 2. They both are alkaline earth metals and contain valency as 2 and hence, placed in group 2.

c. 26Fe, 19K, and 20Ca all belong to the 4th period. Moving left to right across a period, atomic radius usually decreases. Hence, K has the biggest atomic size as compared to 20Ca and 26Fe.

Ans.9

a. In C2H6 total no. of covalent bonds are 7.

b. Homologous means a difference of CH2 in any two molecules and in C2H6 and C3H8 there is a difference of CH2 molecule. Hence they are homologous.

OR

a. Isomers are the elements, of the same molecular formula, but different structural formula. They have the some formula, but their structure are different.

c. because they will have the same structural formula.

Ans. 11. 

a. A parallel circuit divides the current through the electrical gadgets. The total resistance in a parallel circuit is decreased. This is helpful particularly when each gadget has different resistance and requires different current to operate properly. 

b. Due to decrease in length of the wire the resistance got decrease hence more current could flow through the wire. So water boiled in less time.

a. a. Wire A would have higher resistivity. V = IR states that graph of A is with a high slope hence its R is more.

b. Given parameters

The resistance of the electric heater (R) = 8 Ω

Current drawn (I) = 15 A

Time = 2 hrs

T = 120 min x 60

Time (T) = 7200 secs

The rate of heat produced by the device in terms of power is expressed as

P= I2R

P = 15 x 15 x 8

P = 1800 watt

Answer

P= 1800 watt

OR

a. 12 ohm

b. 0.5 A

c. 7.2 x 0.5 = 3.6V

Ans. 13.

a. The flow of energy in food chain in unidirectional because the sun is the only source of energy for all ecosystems on earth. Then the energy is captured by the autotrophs does not revert back to the sun. Therefore, in the food chain, the energy moves progressively through various trophic levels. The energy is no longer available to the previous trophic levels. 

b. According to the law of food chain, only 10% of energy gets transferred to next level in food chain.

Gross (energy) = 10,000J

Dear (Energy) = 10% of 10,000 = 1000 J

Lion (energy) = 10% of 1000J = 10/100 x 1000 = 100 J.