**Solutions of Class 10 Science Important Questions for Term 1 and Term 2 CBSE Board exam**

**CBSE Class 10 Science Exam 2019-20: Important questions** with answers for most recent test design. Here we are giving **significant solutions of important questions** to the changed syllabus in **CBSE Class 10 Science Exam 2019-20.** Practicing these **important questions** and inspecting their **answers** will without a doubt help you plan better for the **exam.**

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**Finding the roots of the polynomial by the complete square method**

**Addition subtractions multiplication and division of of polynomials**

**Q1 (a) List any two changes which take place when oily food get oxidized.**

**(b) Mention a measure which prevents or slows down its oxidation.**

(a) Answer- modifications prominently occurs when food gets oxidized are (i) Bad smell (ii) Bad taste

(b) Answer- Anti-oxidants are introduced to meals which prevent it to get oxidized for instance ascorbic acid(vitamin c), vitamins A and E, vinegar also works as antioxidants as well as antifungal and antibacterial that’s why it’s frequently used in pickle and different packaged meals.

**Q2.Out of the two metals P and Q, P is less reactive than Q. Suggest an activity to arrange these metals in the order of their decreasing reactivity. Support your answer with a suitable chemical equation.**

Answer-Dissolving the metal Q in the salt solution of P, Q displaces P which shows that Q is more reactive than P. If we dissolve P inside the salt solution of Q, Q couldnโt get replaced byย ย P, so Q is more reactive than P.

Q + salt solution of P โP + salt solution of Q

**P + salt solution of Q โ No reaction**

**Q3.Mention the condition under which charges can move in a conductor. Name the device which is used to maintain this condition in an electric circuit.**

Answer-Charges can flow if there’s a difference of electric-powered pressure or potential difference across the ends of a conductor.

Electric cell or a battery, electric generator and dynamo maintains potential differences across the conductor or in the circuit that allows the flow of charge.

**Q4. YX Magnetic field lines are shown in the given diagram. A student makes a statement that magnetic field at X is stronger than at Y. Justify this statement. Also, redraw the diagram and mark the direction of magnetic field lines.**

ย Answer-The intensity of the magnetic field lines traces is greater on the ends of the magnet so the observation of the student that the magnetic field is more potent at x in comparison to at Y is all right.

The magnetic field lines originate from the north pole and merge into the south pole, so the direction of the magnetic field might be from north to south pole as shown bellow.

**Q5.Write the balanced chemical equation for the following reaction and identify the type of reaction and define it. โIron III oxide reacts with Aluminium and gives molten iron and aluminum oxideโ**.

Answer-

The reaction is generally referred to as thermite for the considerable amount of heat produced. The iron produced via the reaction is molten.

**Q6 Name the following :**

**(a) A metal which is preserved in kerosene**

**(b) A lustrous colored non-metal**

**(c) A metal which can melt while kept on the palm.**

**(d) A metal, which is a poor conductor of heat.**

Answers-

(a) Sodium, lithium & Potassium are preserved in kerosene.

(b) Iodine &Diamond are lustrous colored non-metals.

(c) Gallium & Caesium have the lowest melting point of 29.8ยฐ and 28.5ยฐ respectively which could melt while kept on the palm.

(d) Mercury & Lead are metals which are poor conductor of heat.

**Q7.An electric heater rated 800 W operates 6 h/day. Find the cost of energy to operate it for 30 days at ` 3.00 per unit.**

Answer-Hours of consumtion for 30 days = 30 ร 6 = 180 h

800 W = 800/1000 = 0.8 KW

Electric energy = power ร Time

= 0.8 KW ร 180 h

= 144 KWh ( 1KWh = 1 unit)

Cost/unit = โน3.00

value of energy = 144 kWh ร โน3.00 / kWh

= โน432

**Q8 Draw magnetic field lines produced around a current carrying straight conductor passing through cardboard.**

Answer.

**Q9.How will the strength of the magnetic field change, when the point where the magnetic field is to be determined, is moved away from the straight wire carrying constant current? Justify your answer.**

Answer- The direction of the magnetic field around the current carrying conductor is perpendicular to the direction of current through the conductor,the magnetic field lines produced around it can be shown by the concentric circles around it, The strength of the magnetic field decreases when the point moves away from the straight wire carrying constant current.

**Q10.How many covalent bonds does ethane has ?**

Answer. Ethane has 1 C-Cย bond and 6ย C-H bonds,in total ethane has 7 covalent bonds.

**Q11.In which form Hโ ย ion exists in the water ?**

Answer.H^{+}ions exist in the water in the form of HโO^{+}(hydronium) ions.

**Q12. Write Snell’s law.**

Answer. When a light ray passes from one medium to another medium the ratio between the sine of incident angle and refracted angle is constant.

sin i/sin r = Constant, where i is incident angle and r is refracted angle

**Q13.Which liquid fills the space between eye lenses and retina.**

Answer.The space between eye lenses and retina is called the vitreous chamber which is filled with a transparent jelly-like fluid vitreous humor.

**Q14.What is electromagnetic induction?**

Answer. When a conductor moves in a magnetic field,a voltage is produced across it,it is a phenomenon used in the dynamo in the production of electricity. First time it was discovered by Faraday.

**Q15.State the modern periodic law.**

Answer. Properties of the elements are the periodic function of their atomic number,this is the law modern periodic table is based upon.

**Q16. What is short-circuiting?**

Answer. When two electrical wires come in contact with each other, their net resistance become law and high current flows through the circuit, due to high current, excess heat produced blow the circuit. The path of the circuit becomes shorter that’s why this problem is given the name short circuit.

**Q17.What is the power of bulb rated at 2.5 volts,500 mA?**

Answer.As we know P = V ร I, where P=Power,V =Voltage, I=Current

V=2.5v, I=500 mA= 500/1000=0.5 A (1A =1000mA)

P = 2.5v ร 0.5A = 1.25W

Therefore the power of the bulb =1.25W

**Q18.An object is kept at a distance of 5 cm in front of a convex mirror of focal length 10 cm.Give the position,magnification and nature of the image formed.**

Answer. the distance of the object (u)= โ5 cm, focal length(f) = +10 cm(Focal point ofย convex mirror lies behind the mirror), distance of the image formed=v =?

Applying the mirror formula,we have

The position of image formed is 3.33 cm behind the mirror.

**Q19.What is meant by the magnetic field lines ? Draw the pattern of the magnetic field lines due to a current-carrying circular loop of wire.**

Answer. Magnetic field lines show the direction and strength of the magnetic field around a magnet,if a small compass is used to map out across a magnet the needle indicating north pole point out the direction of the magnetic field, it could be seen that these field lines originate from the north pole and merge into the south pole ,we can observe these field lines if we place a bar magnet on a plane of paper containing iron dust, the iron dust aligned into the form of the curved lines, these lines are known as magnetic field lines. Field lines show the direction and intensity of the magnetic field.

**Q20.What is the chemical formula of Plaster of Paris? How is it prepared? State the common and the chemical names of the compound formed when Plaster of Paris is mixed with water.**

Answer.the chemical formula of Plaster of Paris

Plaster of Paris is prepared by heating gypsum up to 300ยฐc,ย lossing ย molecule of water it forms ย Plaster of Paris.

**Giypsumย ย ย ย ย ย ย ย ย ย ย ย ย ย ย POP**

When POP is mixed with water it is crystallized to form Gypsum which is a hard substance**.**

**POPย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย Gypsum**

The common name of CaSO4.2H2O is Gypsum and its chemica name is Calcium Sulphate Dihydrate

**Q21.What is the Chlor-alkali process?Why is it so called?**

Answer. The electrolysis of an aqueous solution of sodium chloride is known as Chlor-alkali process, it is called Chlor-alkali process because the products formed during this process are NaOH(Caustic soda) an alkali used in soap industry and chlorine(Chlor) gas used as antiseptic for improving quality of water.The hydrogen gas is also produced in this process.

**Q22.How does the electronic configuration of an atom related to its position in the modern periodic table ?**

Answer.Electronic configuration of an atom determines the valancy of element ,the valance e’s of atom shows the last digit of group number and number of orbital shows the period of atom.As an example Na(11)-2,8,1ย Cl-2,8,7, the group number of sodium is one and its period is 3 and group number of chlorine is 17 and its period is 3.

**Q23.A bulb is rated at 5.0 V-100mA; calculate its (a) Power, and (b) Resistance.**

Answer. Power(P) = Volage(V) ร Electric Current(I)

V = 5.0V, I = 100 mA= 100/1000 =0.10A

P= V ร I = 5.0 ร 0.10 = 0.50W

Voltage(V) = I ร R(Ohmโs law)

R = V/I = 5.0/0.10 =50ฮฉ

Therefore the power of bulb is 0.50W and its resistance is 50ฮฉ.

**Q24. Write any two factors on which strength of two induced current depends.**

Answer. The induced current depends on the following factors.

- The strength of magnetic field.
- Motion of the conductor.

**Q26.Give reasons for the following;**

**(a)Metals conduct electricity .**

**(b)Metals generally do not form compounds with hydrogen.**

**(c)Nitrogen gas is used to preserve food.**

Answer.(a) Metals conduct electricity because it contains free electrons in the gaps between its atoms, these free electrons exist only in metals because e’s in it are not bound by any chemical bond like a covalent or ionic bond, so these e’s can move freely within the metal.When an electric potential difference is generated in its both ends these e’s moves from one end to another end generating a current through the conductor.

(b)Metals and Hydrogen both are positively charged ,so neither they can form ionic bond nor a covalent bond in the formation of the compound,but few of metals like Na,K,mg and Ca are most reactiveย so these atoms forces hydrogen to form their hydride.

(c) In the packaging material nitrogen gas is filled because it doesnโt react with oily substance available in the food moreover, it displaces oxygen available inside the packet and prevents the food to be oxidized.

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