[5 marks Questions]

Question 15 Marks

Discuss the important characteristics of covalent compounds.

Answer

1. Covalent compounds consist of molecules. Covalent compounds do not have any ions. Therefore, they consist of molecules. For example, $H _2, Cl _2, H _2 O , NH _3 etc$.
2. Covalent compounds are liquids or gases in nature. We have studied that the ionic compounds are crystalline solids. But only a few covalent compounds are solids (e.g. sugar, glucose, iodine). These are mostly liquids (water, ethyl alcohol) or gases (oxygen, hydrogen, ammonia) at room temperature. Actually, the attractive forces in covalent molecules are weak and these molecules are not as close lo one another as the ionic solids.
3. Covalent compounds have low melting and boiling points. As covalent molecules do not have ions, the attractive forces among them are weak. Therefore, the covalent molecules can be easily separated from each other. In other words, they have low melting and boiling points.
4. Covalent compounds do not conduct electricity. Covalent compounds normally do not conduct electricity. Some of them are poor conductors of electricity. The current is carried by the ions. As covalent compounds do not have ions, these are poor conductors of electricity.
5. Covalent compounds are insoluble in water. Covalent compounds generally do not dissolve in water. They are soluble in alcohol, ether, benzene etc. which are called organic solvents. However some of them such as ammonia and ethyl alcohol are water soluble.

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Question 25 Marks

Given below is a diagram of the human endocrine system.

Using the given diagram, answer the following questions:
i. How pituitary gland regulates the growth of the body?
ii. Which hormone is responsible for the carbohydrate, protein, and fat metabolism in the body?
iii. Which pair of glands prepare the body to deal with emergency situations?
iv. Which gland secretes insulin and what does it do in the body?
v. What is the function of endocrine glands?

Answer

i. Pituitary gland secretes growth hormone that regulates the growth and development of the body.
ii. Thyroxin hormone is secreted by the thyroid gland that is responsible for the carbohydrate, protein, and fat metabolism in the body.
iii. A pair of adrenal glands located on kidneys prepares the body to deal with stress, anxiety, and emergency situations.
iv. The pancreas secretes insulin that regulates our blood sugar levels.
v. Endocrine glands are ductless glands that secrete hormones to regulate many body functions, including growth, development, reproduction, and metabolism.

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Question 35 Marks

An object $2 \ cm$ high is placed at a distance of $16 \ cm$ from a concave mirror which produces a real image $3 \ cm$ high.
$(i)$ Find the position of the image.
$(ii)$ What is the focal length of mirror?

Answer

Object height, $h = +2 \ cm$
Image height, $h' = - 3\ cm$ real image hence inverted
Object distance, $u = - 16\ cm$
Image distance, $v -?$
Focal length, $f =?$
$(i)$ Position of image
From the expression for magnification
$ m=\frac{h^{\prime}}{h}$
$=\frac{v}{u} $
We have, $v =-u \frac{h^{\prime}}{h}$
Putting values, we get $v =-(-16) \times \frac{-3}{2}$
$v=-24 \ cm$
The image is formed at distance of $24 \ cm$ in front of the mirror $($negative sign means object and image are on the same side$).$
$(ii)$ Focal length of mirror
Using mirror formula, Putting values,
we get Using mirror formula, $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$
Putting values, we get $\frac{1}{f}=\frac{1}{-16}+\frac{1}{-24}$
$=-\frac{3+2}{48}$
or $f=-\frac{48}{5}$
$=-9.6 \ cm$

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Question 45 Marks

How are the images formed when an object is moved from infinity to the convex lens?

Answer

Object at Infinity. When object is at infinity, a real image is formed at F on the other side of the lens

Object at infinity. Image at F on the other side of lens.
However if the rays are parallel to themselves but not parallel to principal axis, then these rays after refraction will form image at focus F' and not at principal focus F.

Object at infinity, rays parallel to themselves but not parallel to principal axis. Image is formed at F', the focus on the other side of lens. Object beyond 2F. When the object is beyond 2F, a real, inverted, diminished image is formed between F and 2F.

Object beyond 2F, real, inverted, diminished image between F and 2F. Object at 2F. When the object is at 2F, a real, inverted
image of the same size is formed on the other side of the lens at 2F as given in Fig.

Object at 2F, image at 2F on the other side of the lens. Image is of size same as that of the object. When the object is between F and 2F, its real, inverted, magnified image is formed on the other side of the convex lens as shown in fig.

Object between F and 2F real, inverted, magnified image is formed beyond 2F on the other side of lens. Object at F. When object is placed principal focus, a real, inverted, very highly magnified image is formed at infinity.

Object at F, a very highly magnified, real, inverted image is formed at infinity.
Object between F and C. When an object is placed between principal focus and optical centre of the lens, virtual, erect, magnified image is formed on the same side of the lens.

Object between F and C; a virtual, erect, magnified image is formed on the same side.

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Question 55 Marks

Explain various steps of budding in yeast.

Answer

Budding in yeast: Most of the common yeasts reproduce by budding. The process of budding occurs under normal conditions when the yeast cells are growing in sugar solution. Saccharomyces usually reproduce by budding.

In the process, each cell gives rise to one of more tiny outgrowths which gradually increase in size as large as the mother cell itself. Ultimately, it is cut off from the mother cells by a constriction at the base and can lead a separate existence. The nucleus divides amitotically during budding and one daughter nucleus passes in the bud and the other remains in the mother cell. The nuclear membrane persists throughout the nuclear division. The budding may be repeated by the daughter cell while still attached to the parent cell, resulting in the formation of one or more chains and even subchains, called pseudomycelium. The cells ultimately become separated from one another and lead independent life.

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Question 65 Marks

Discuss the formation of covalent bonds in molecules of
$i.$ Ammonia
$ii.$ Ethylene
$iii.$ Carbon dioxide.

Answer

$i.$ Covalent bonds in ammonia $(NH_3)$ molecule: The atomic number of nitrogen is $7.$ Its electronic configuration is $2, 5$. This means that nitrogen atom has five valence electrons. In order to have eight electrons in the valence shell, the nitrogen atom shares three electrons with the electrons of three hydrogen atoms. Thus, nitrogen atom gets linked to three hydrogen atoms by three covalent bonds. The formation of ammonia molecule may be shown as follows:

$ii.$ Covalent bonds in ethylene $(C2H_4)$ molecule: Ethylene molecule has two carbon atoms. Each carbon atom shares two electrons with the two hydrogen atoms. At the same time, both the carbon atoms mutually share two electrons each. Thus both the carbon atoms get linked by double bond. Each carbon atom also gets linked to two hydrogen atoms by single bonds. The formation of ethylene molecule may be shown as follows:

$iii.$ Covalent bonds in carbon dioxide $(CO_2)$ molecule: Carbon atom has four electrons. Each oxygen atom has six valence electrons $(2, 6).$ The carbon atom shares its electrons with the electrons of the two oxygen atoms. As a result, the carbon atoms gets linked to the oxygen atoms by double bonds. The formation of carbon dioxide molecule may be shown as follows:

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