PABSON SEE PRE BOARD EXAM-2078 (Answer Keys and Science Marking Scheme)

Tek

15 Mar, 2022

Science Marking Scheme

This marking scheme is not a complete set of answers but a set of answer keys. The examiners can use their discreet and examine the answer copies.

Q. No.	Answer Keys	Marks
Q.1. a	The mutual force of attraction between any two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance from their centres	1
b	The ratio of the density of a substance to density of pure water at 4⁰C	1
c	Any two causes: population growth, urbanization, etc.	2 x 0.5
d	Amount of heat required to increase the temperature of a substance by 1⁰C	1
e	An inverter converts ac into dc, stores it in a battery, and converts it into ac again when power is cut off	1
f	Transition elements are the elements lying in between IIA and IIIA groups in the modern periodic table, which feel valence electron in d-sub-shell	1
g	Magnesium hydroxide	1
h	Aluminium	1
i	Silica, Sodium Carbonate and Calcium Carbonate	1
j	Strongest of all-natural fibre, highly elastic, does not decay, etc.	2x0.5
k	Adrenal gland	1
l	3.5 – 7.2 mg/dl	1
m	(45 + XX)/(45 + XY)	1
n	Sudden chromosomal change that causes a change in morphology and physiology of an organism	1
o	Palaeozoic era	1
Q.2	The density of the egg is more than density of pure water due to which its weight becomes more than the upthrust exerted by water. Likewise, the density of the egg is less than the density of salt solution due to which the weight of the egg becomes less than the upthrust exerted by water.	2
Q.3	Renewable: can be replenished in short period of time, biomass Non-renewable: takes long time to be replenished, coal	2x1
Q.4	Solution, Given, Mass of water (m) = 5 kg SHC (s) = 4200 J/kg⁰C Change in temperature (dt) = 30⁰C – 20⁰C = 10⁰C Amount of heat (Q) = ? Now, Q = smdt Or, Q = 4200 x 5 x 10 Or, Q = 210000 J	Given (0.5) Formula (0.5) Calculation (0.5) Answer with unit (0.5)
Q.5	Convex It converges the rays of light coming from a near object. Then, the eye lens converses them so that the image is formed on the retina otherwise converges behind the retina.	0.5 + 1.5
Q.6	Catalyst: increases or decreases the rate of chemical reaction, iron Promoter: promotes the rate of chemical reaction, molybdenum	2x1
Q.7	Sodium acetate is formed by the reaction of a strong base, NaOH and a weak acid, CH₃COOH	2
Q.9	Soap: raw materials - animal fat or vegetable, biodegradable, etc. Detergent: raw materials – hydrocarbons, non-biodegradable, etc.	2x1
Q.10	Source of vitamin B, prevents heart disease, etc.	2x1
Q.11	A genetic disorder caused due to the presence of blood clotting factor deficiency gene in chromosome Excessive internal/external bleeding, spontaneous nosebleeds, etc.	1 2x0.5
Q.12	Plants that do not produce viable seeds can be reproduced. The plants obtained by this method produce flowers and fruits earlier than the ones obtained from seeds.	2x1
Q.13	By reducing the use of chemical fertilizers By disposing of the radioactive wastes properly	2x1
Q.14	Meteors are pieces of metallic or rocky matter falling down from space to the earth's surface at high speed. Due to their high speed, there occurs massive friction between them and air. As a result, they burn during their journey and look like stars.	2
Q.15	Solution, Given, Mass of the earth (M) =6×10²⁴ kg Radius of the earth (R) =6400 km=6400000 m Gravitational constant (G) =6.67×10^-11 Nm²/kg² Mass of stone (m) =50 kg Acceleration due to gravity (g) =? Weight of stone (W) =? Now, g= GM/R² Or, g= 6.67×10^-11×6×10²⁴/ (6400000)² Or, g= (40.02×10¹³)/ 4.096×10¹³ Or, g=9.77 m/s² Then, W=mg Or, W=50 ×9.77 Or, W=488.5 N	Given (0.5) For 'g' Formula (0.5) Calculation and unit (1) For W Formula (0.5) Calculation & unit (0.5)
Q.16	correct drawing Solution, Given, Focal length (f) =3 Object distance (u) =7.5 cm Image distance (v) =? Now, 1/f= 1/u+1/V Or, 1/3=1/7.5+1/v Or, 1/V= 1/3-1/7.5 Or, 1/V= (2.5-1)/7.5 Or, V=5 cm	1 Given (0.5) Formula (0.5) Calculation and Unit (1)
Q.17	a) VII'A' b) Fluorine. F and Cl have 7 electrons in their valence shell. Their reactivity tendency of gaining one electron to be stable. The atomic size of F is lesser than that of Cl due to which F can more easily gain electrons than Cl. c) Mg+ Cl₂→MgCl₂	0.5 0.5 1 1
Q.18	An atom or a group of atoms that determines the chemical nature of an organic compound Glycerol is formed.	1 1.5 0.5
Q.19	A cross of the organisms involving a pair of contrasting characters	1 Cross (1) Ratio (1)

Q.20	a) B – Pulmonary Vein, F – Pulmonary Artery b) Blood is purified, i.e. exchange of oxygen and carbon dioxide takes place. c) Oxygenated in E and deoxygenated in F	1 1 1
Q.21	a) Electromagnetic induction b) Needle shows deflection because magnetic flux is linked with closed-circuit changes and emf is produced. c) Needle shows no deflection because magnetic flux linked with closed-circuit does not change and no emf is produced.	1 1.5 1.5
Q.22	The chemical reaction of the Principle: CaCO2 + 2 HCl →CaCl2 + H2O + CO2 ↑ Ammonia is lighter than air and highly soluble in water.	Drawing 1 labelling of any two major parts 2x0.5 2x0.5 1
Q.23	a) Pancreas b) Insulin and glucagon c) Hypoglycemia/hyperglycemia or diabetes (I or II) d) This gland is a mixed or heterocrine gland because it acts as both endocrine as well as an exocrine gland. As an endocrine gland, it secretes hormones: insulin and glucagon and as an exocrine gland, it secretes juice: pancreatic juice.	0.5 1 0.5 2
Q.24	The earth is surrounded by the atmosphere. It allows the solar radiation of a short wavelength to enter it but does not allow the reflected radiation with a long wavelength to escape from the atmosphere. As a result, solar heat is trapped in the atmosphere. Any four effects: - Respiratory diseases - Blurred sight - Skin allergy - Decrease in haemoglobin efficiency	2 4x0.5