a/r test 3

in each of the following questions, a statement of assertion is given and a corresponding statement of reason is given just below it. of the statements, mark the correct answer as

a) both A and R are true and R is the correct explanation of A
b) both A and R are true and R is not the correct explanation of A
c) A is true and R is false
d) both A and R are false

biology:

1.
A: mast cells in human body releases excessive amount of inflammatory chemicals which causes allergic reactions
R: allergens in the environment on reaching human body stimulate mast cells

2.
A: holoblastic cleavage with almost equal size blastomeres is a characteristic of placental animals
R: eggs of most mammals, including humans, is centrolecithal

3.
A: in plant tissue culture, somatic embryos can be induced from any plant cell
R: any viable plant cell can differentiate into somatic embryo

4.
A: in a food chain members of successive higher levels are fewer in number
R: number of organisms at any trophic level depends upon the availability of organisms which serves as food

5.
A: leaf butterfly and stick insect show mimicry to dodge their enemies
R: mimicry is a method to acquire body colour blending with the surroundings

physics:

1.
A: the resistivity of a semiconductor increases with temperature
R: the atoms of semiconductor vibrate at larger amplitude at higher temperature, thereby increasing resistivity

2.
A: when a beetle moves along the sand within a few centimetres of scorpion, the scorpion immediately turns and dashes towards it
R: when a beetle disturbs the sand, it send pulses along the sand's surface through which scorpion detects the beetle

3.
A: it is hotter over the top of a fire than at the same distance on the sides
R: air surrounding the fire conducts more heat upwards

4.
A: the amplitude of an oscillating pendulum decreases with time
R: the frequency also decreases with time

5.
A: microwave communication is preferred over optical
R: microwaves provide larger bandwidth

chemistry:

1.
A: NF3 is a weaker ligand than N(CH3)3
R: NF3 ionises to F- ions in aqueous solution

2.
A: PbI4 is more stable than PbI2
R: iodide stabilizes higher oxidation states

3.
A: alkyl benzene is not prepared by friedel craft alkylation of benzene
R: alkyl halides are less reactive than acyl halides

4.
A: hydroxyketones are not directly used in grrignard reaction
R: grignard reagent reacts with hydroxyl group

5.
A: cis-1,3-dihydroxycyclohexane exist in boat conformation
R: in the chair form, there will not be H-bonding between the two hydroxyl groups

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