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The modem periodic law states that, “The physical and chemical properties of the elements are periodic function of their atomic numbers.”

(b)The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitais in a d-subshell.

(a) nuclear charge (Z).

(c) principal quantum number

In the modern periodic table, each period begins with the filling of a new shell. 

Therefore, the period indicates the value of principal quantum number.

Thus, option (c) is correct.

2s and 2p orbital are possible.

• Yes, I agree that the aquatic ecosystem of coringa mangrove region would be less saltier than the bay. 
• Because aquatic ecosystem of coringa mangrove region receive fresh water from Coringa and Gaderu rivers. 
• Distributories of Gautami, Godavari river and number of small rivers and canal transverse this mangrove ecosystem. 
• Hence Coringa mangrove region would be less saltier than bay.

Benthic zone is absent in fresh water ecosystem when compared to marine ecosystem.

Abyssal zone is absent in fresh water ecosystem.

Adaptations required to survive in abyssal zone are : 

1. The animals should have wide mouths and huge curved teeth which prevent escape of any prey.

2. Absence of skeleton, flattened bodies are required. 

3. Animals should have special structures that produce light on their bellies, around their eyes, and at the sides of their bodies. 

4. The animals should show bioluminescence in the dark waters.

• Nearby pond or lake consists of three zones namely littoral zone, limnetic zone, and profundal zone. 
• In the topmost littoral zone, the edge of a water body is home to snails, insects, several crustaceans, fishes and amphibians, and the eggs and larvae of dragonflies. 
• Predators present are tortoise, snakes, and ducks.
• Adaptations : Several organisms have well developed sight, usually have dull and greyish bodies, and are fast swimmers. 
• Limnetic zones contains fresh water fish, crustaceans like daphnia, cyclops, and small shrimps are present. 
• Floating- plants like water hyacinth, wolfia, pistia along with algae are present. 
• Adaptations seen in the plants this zone are presence of air space, leaves covered with wax, etc. 
• In the profundal zone scavengers and predators for example crustaceans, crabs, fishes like eels and snails, turtles are present. 
• They adapt themselves by feeding on dead animals that settle down.

1. The saliny of water in marine ecosystem is 3.5% whereas it is 1.8% in fresh water. 

2. Marine ecosystems are huge and they make up about three-fourths of the earths surface.

3. The number of organisms present in marine ecosystems are more when compared to fresh water ecosystem.

s-orbital is non-directional orbital.

B) 1 – c, 2 – a, 3 – b

Electron density in s-orbital is equal in all direction while it dumble shaped along one axis in p- orbitals.

s- orbital is non-directional. 

s-orbital is spherically symmetrical i.e., it is non-directional.

• Yes, Murrel and Rohu be able to live in the coringa ecosystem. 
• Because coringa ecosystem gets fresh water from rivers coringa, Gaderu and distributories of Gautami, Godavari rivers. 
• If the salinity of the water in the coringa ecosystem increases, the water enters the body of fresh water fishes.
• The water can be excreted in the form of urine, but to maintain a suitable salt balance fresh water fish need to reabsorb salt through the kidneys and salt collecting cells in gills.

• Yes, marine water fishes drink more water than fresh water fishes. 
• Because several marine fishes have a lower internal salt concentration than that of the water they swim in. 
• So they tend to dehydrate as water is lost by osmosis.
• To compensate, they drink large amount of water and excrete the salts both via their kidneys and through highly specialised cells in the gills.

B) Marine fishes

₂₄Cr = 2, 8, 13, 1

= 1s²,2s²2p⁶,3s²3p⁶3d⁵,4s¹

\(\therefore\) Number of unpaired electrons in Cr in ground state = 6

1. Its atomic number is 11 

2. It is s-block element 

3. It is in 3rd period ’ 

4. It is in 1st group 

5. Its valency is 1 

6. Number of valency electrons are 1 

7. It can form uni positive ion 

8. It can form ionic bond, 

9. It is metal.

Quantization of energy means the energy of energy levels can have some specific values and not all the values.

S – orbital is spherically symmetrical i. e it is non – directional.

• According to Hund’s rule of maximum multiplicity “Pairing of electrons in the orbitals belonging to the same subshell does not occur unless each orbital belonging to that subshell has got one electron each.”
• Oxygen has 8 electrons. The first two electrons will pair up in the Is orbital, the next two electrons will pair up in the 2s orbital and this leaves 4 electrons, which must be placed in the 2p orbitals.
• Each of the three degenerate p-orbitals must get one electron of parallel spin before any one of them receives the second electron of opposite spin. Therefore, two p orbitals have one electron each and one p-orbital will have two electrons.

Thus,

The electronic configuration of oxygen is written as 1s² 2s² 2p_x² 2p_y¹ 2p_z¹ and not as 1s² 2s² 2p_x² 2p_y² 2p_z⁰.

C) Limnetic zone

Electronic configuration = 1s²,2s²2p⁶,3s²,3p⁶

No. of electrons = 18

Atomic number = 18 + 2 = 20

\(\therefore\) Ion is Ca²⁺

Correct option is a. Hund’s rule

Quantization of energy means the energy of energy levels can have some specific values and not all the values.

(i) n = 4,   1 = 2

\(\therefore\) Orbital is 4d.

(ii) n = 1,  1 = 0

\(\therefore\) Orbital is 1s.

(a) 2p

(b) 4s

(c) 5f

(d) 3d

(a) 1s

(b) 3p

(c) 4d and

(d) 4f

The region where the probability of finding an electron is zero i. e. ψ² = 0

1s electron being close to the nucleus experiences more force of attraction than

2s– electron which is away from the nucleus.

(i) Principal quantum number (n), and

(ii) Magnetic quantum number (m).

i. 2p 

ii. 4d 

iii. 3d

Greater the penetration of the electron present in a particular orbital towards the nucleus, more will be the magnitude of the effective nuclear charge. Based upon this criterion:

(i) 2s electron will experience more effective nuclear charge.

(ii) 4d electron will experience more effective nuclear charge.

(iii) 3p electron will experience more effective nuclear charge.

For the 3d orbital :-

Principal quantum number (n) =  3

Azimuthal quantum number (l) = 2

Magnetic quantum number (ml) =

 – 2, – 1, 0, 1, 2

1. 2KHCO. + H₂SO₄ (dil) → K₂SO₄ + 2H₂O + 2CO₂ 

2. 2NaNO₃ + H₂SO₄ (cone) → Na₂SO₄ + 2HNO₃

Many diseases are caused by contaminated water. The drinking water should be cleaned by boiling it. Nowadays, filters are also installed in the houses to purify water.

Na₂SO₃ + H₂SO₄ (dil.) → Na₂SO₄ + H₂O+ SO₂ ↑

Purification of Nickel by Mond's process:-

Impure Nickel is treated with Carbon monoxide at 60-80°C when volatile nickel carbonyl is formed which is decomposes to give pure nickel at 180°C

Ni + 4CO → Ni(CO)₄ + Ni → 4CO

Impure                         Pure

Platinum or Vanadium pentoxide.

Contact process.

Correct answer is (B) 0

In the contact process for the manufacture of sulphuric acid, the equations for the conversion of sulphur trioxide to sulphuric acid are

SO₃ +H₂SO₄ (conc.) H₂S₂O₇

(oleum or pyrosulphuric acid)

H₂S₂O₇ + H₂O → 2H₂SO₄

1. S + 6HNO. [cone.] → 6NO₂ + 2H₂O + H₂SO₄ 

2. Cl₂ + SO₂ + 2H₂O → 2HCl + H₂SO₄ 

3. 3SO₂ + 2HNO₃ + 2H₂O → 3H₂SO₄ + 2NO

Hydrogen sulphide (H₂S).

(i) Sodium ions and hydroxide ions.

(ii) Carbonic add molecules, carbonate ions and hydronium ions.

(iii) Sugar molecules and water molecules.