Electronic configuration of nitrogen is 2,5.

A nitrogen atom requires three electrons to achieve octet configuration. Thus in a nitrogen molecule, two nitrogen atoms share three electrons from each of the atoms to attains octet configuration. Hence, three electron pairs are shared between two nitrogen atoms forming three covalent bonds. Hence, nitrogen is also called a trivalent compound.

Effervesence means escaping of gas with bubbles and hissing sound like CO₂ escapes from soda water or coke bottle when opened.

Centre of curvature:

• The reflecting surface of a spherical mirror forms a part of a sphere. The sphere’s centre is called as centre of curvature.
• It is represented by the letter C.
• The centre of curvature is not a part of the mirror. It lies outside its reflecting surface.
• The centre of curvature of a concave mirror lies in front of it.
• However, it lies behind the mirror in case of a convex mirror.

In total, 118 elements have been identified. The first 94 occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. Technetium was the first artificially produced element. It was isolated by Carlo Perrier and Emilio Segrè in 1937. Technetium was created by bombarding molybdenum atoms with deuterons that had been accelerated by a device called a cyclotron.

Acids that give high concentration of H+ ions on ionisation in aqueous solution are said to be strong acids and acids which give less H+ ions on ionisation in aqueous solution are said to be weak acids. Strong acids dissociate fully in water to produce the maximum number of H + ions. This means if you had one mole of hydrochloric acid (HCl) molecules, they would all 'split' to form one mole of H + ions and one mole of Cl – ions. Weak acids, such as ethanoic acid (CH 3COOH), do not fully dissociate.

A biodegradable material or substance can be defined as a material which can be decomposed easily by bacteria or any other natural organisms and not being the part of pollution.

Biodegradable wastes are the waste materials which are and can be easily degraded by natural factors like microbes (e.g. bacteria, fungi and few other), abiotic components like temperature, UV, oxygen, etc. few examples of such wastes are kitchen wastes, food materials, and other natural wastes

A N S W E R 
C o n v e x  mirror always forms a virtual, erect and diminished image of the object placed at any position in front of the mirror.

Biodiversity is “the variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems, and the ecological complexes of which they are part; this includes diversity within species, between species, and of ecosystems.” It is the foundation of life on Earth. Three successful approaches to protecting biodiversity are captive breeding,laws and treaties, and habitat preservation. the number of different species in an area. A species that influences the survival of many others in an ecosystem.

We find that the child's image in the magic mirror has
1. Head bigger and hence the mirror must be a concave mirror. A concave mirror here is producing an enlarged and erect mirror.
2. The middle portion unaltered and hence the middle part of the mirror must be a plane mirror.
3. The bottom part of the mirror produces a smaller image of the legs. The image is smaller since it is produced by a convex mirror. The convex mirror produced the erect and diminished image.
 

A Concave mirror is also called a converging mirror, has a reflecting surface away from the incident light.

Plane mirror is a flat reflecting surface where angle of reflection is equal to angle of incidence.

Convex Mirror is also called the diverging mirror.

Now according to the question at the top it is concave mirror because the boy finds the image bigger it means converging image, on the middle part it is found the image is of same size so it is plane mirror and at the bottom the image becomes smaller that is the image diverges so it is convex mirror.

Limitations of the Mendeleev periodic table :

• Elements with large differences in properties were included in the same group. for example, hard metals like copper and silver were included along with soft metals like sodium and potassium.
• No proper position could be given to the element hydrogen. In the periodic table, the location of hydrogen is uncertain. It was put with alkali metals within 1A class, but certain hydrogen properties are close to those of halogens. So, it can also be put for halogens in the band.
• The increasing order of atomic mass was not strictly followed throughout. For example in cobalt and nickel & Tellurium and Indium.
• As isotopes are atoms of the same element having different atomic masses, they should have been given different positions while arranging them in the order of atomic mass. But this was not done.

Pre Boards Make Students Serious for Board Exams

The only purpose of grilling session in pre-board exam is to bring out seriousness amongst the candidates. The exams are planned to offer a demo experience of the board exams.

The question paper exposes students to various types of difficulties they may face while attempting the actual answers. The exam is like a practice session to make students serious for upcoming board exams. The result of these internal exams will help you realize which subjects require more attention.

Help Track Your Performance

Pre boards are meant for evaluating your performance. Students can utilize the pre-boards to track their performance. The question paper of pre-board is a replica of board exams.

You must carefully evaluate each subject’s question paper as it will not only help in pinpointing any shortcomings in your revision, but will also further strengthen the areas where you already score well.

But you must not take any stress, even if the results are not good; to make it up for, push yourself harder each day by focusing on the topics in which you lag.

Try not to repeat your mistakes. You should revise seriously. If your pre-board marks are good, then, you should push yourself a little extra to get an excellent score.

(1) It is used as an antacid in medicine to remove acidity of the stomach. (2) It is used in making baking powder. Baking powder is a mixture of baking soda and a mild edible tartaric acid. When baking soda mixes with water,then sodium hydrogen carbonate reacts with tartaric acid to evolve carbon dioxide gas.

• Baking soda (sodium hydrogencarbonate) undergoes reaction with mild edible acid such as tartaric acid to manufacture baking powder. This baking powder on heating undergoes following reaction.

• This carbon-dioxide produced makes bread or cake rise thereby making them soft and spongy.
• Being alkaline it is also an active ingredient in antacids that acts by neutralising the excess acid produced in the stomach.
• It is also used in soda-acid fire extinguishers.

It is in the form of a white powder. When the powder of Plaster of Paris is mixed with water, it becomes hard and solid gypsum. ... In , only half a water molecule is shown as the water of crystallization because two molecules of CaSO4 share one molecule of water

or

Formula of plaster of Paris is CaSO₄.1/2 H₂O

It is not possible to have half a molecule of water.

The formula CaSO₄.1/2 H₂O over here actually means that two molecules of CaSO₄ share one molecule of water.

The formula of plaster of Paris can also be written as 2CaSO₄. H₂O.

Both venae cavae  pass the deoxygenated blood to the right atrium. Blood from the right atrium  enters right ventricle  and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation. Two pulmonary veins  come from each lung and pass oxygenated blood to left atrium . The left ventricle pumps blood into the aorta   which in turn branches and delivers blood to the major body regions and organs.  

Here is the average blood type distribution in the Indian population:

• O+ = 27.85%
• O- = 1.43%
• A+ = 20.8%
• A- = 0.57%
• B+ = 38.14%
• B- = 1.79%
• AB+ = 8.93%
• AB- = 0.49%

Therefore we see that the most common blood group in India is B positive. The second most prevalent blood group in India is O positive.

Fossils are remains or impressions of organisms that lived in the remote past. Fossils provide the evidence that the present animal have originated from previously existing ones through the process of continuous evolution. Fossils can be used to reconstruct evolutionary history of an organism. The distribution pattern of fossils shows that the ancient fossils present in the bottom rocks are simple, while the most recent fossils found in the upper strata are more highly evolved. It means fossils form and become more and more complex as we proceed from earliest to recent rocks. It gives us an idea of time in history when different species were formed or became extinct. Fossil also help to trace the evolutionary history of some animals.

Fossils are remains or impressions of organisms that lived in the remote past. Fossils provide the evidence that the present animal have originated from previously existing ones through the process of continuous evolution. Fossils can be used to reconstruct evolutionary history of an organism. The distribution pattern of fossils shows that the ancient fossils present in the bottom rocks are simple, while the most recent fossils found in the upper strata are more highly evolved. It means fossils form and become more and more complex as we proceed from earliest to recent rocks. It gives us an idea of time in history when different species were formed or became extinct. Fossil also help to trace the evolutionary history of some animals.

Mendel selected true breeding tall (TT) and dwarf (tt) pea plants.When a tall pea plant is crossed with a short (dwarf) pea plant, all the F1 hybrids are tall. (i.e., in this case, the gene causing tallness is dominant while the gene causing dwarfness is recessive.).The trait expressing itself in the hybrid is the dominant one. 

(Mendel’s first law of inheritance states that when a pair of contrasting factors is brought in a hybrid, one factor inhibits the appearance of the other. The one which inhibits is the dominant one and which is inhibited is recessive.) 

A n s w e r
Advantages of adopting preventive methods are:

Helps in maintaining health of women.
Helps in preventing STDs especially AIDS.
Helps in birth control.
Parents can give more attention to children.

Right hand Thumb Rule

If a current carrying conductor is imagined to be held in right hand such that thumb points in direction of current,then curled fingers of hand indicate the direction of magnetic field.

If current flows in upward direction then direction will be anticlockwise.

If current flows in downward direction then direction will be clockwise.

Potential difference (V)= Work done (W) / Charge (q)

On rearranging the above formula we get

Work done (W) = Potential difference X Charge

Put the value of V and q in the above equation, we get

Work done (w) = 6 X 1

Work done = 6 Joules

Therefore, the energy is given to each coulomb of charge passing through a 6 v battery is 6 J.