Explanation

 The maximum number of electrons in an atom is given by the formula:  

Total electrons = 2n²  

For n = 4:  

2(1² + 2² + 3² + 4²) = 2(1 + 4 + 9 + 16) = 2(30) = 60  

But this is a misunderstanding. Each shell holds:

- n=1: 2  

- n=2: 8  

- n=3: 18  

- n=4: 32  

So total = 2 + 8 + 18 + 32 = 60, but this is not per atom.  

If n = 4 is the maximum principal quantum number, then the 4th shell is being filled.  

The maximum number of electrons that can exist in the 4th shell is:  

2n² = 2(4)² = 32

Explanation

A respiratory surface must have a good supply of blood. 

A respiratory surface needs to be thin, permeable, and have a large surface area to efficiently facilitate gas exchange.

However, the crucial aspect is the blood supply.

The proximity of blood capillaries to the respiratory surface allows for the rapid transfer of oxygen from the air to the blood and carbon dioxide from the blood to the air. 

Explanation

 He is very careful. He does not allow his children to drive his car in rush hour traffic.

وہ بہت محتاط ہے۔ وہ اپنے بچوں کو رش کے اوقات میں گاڑی چلانے کی اجازت نہیں دیتا۔

The sentence is in the present tense — indicated by: "He is very careful..."

So, the next part must also be in the present tense.

Explanation

 The part of a cell responsible for protein synthesis is the Ribosomes. 

Ribosomes are the cellular structures where proteins are synthesized by translating mRNA into amino acid chains

Explanation

A permanent change in the genetic structure of a gene is called a mutation. 

A mutation refers to a change in the DNA sequence of a gene, which can lead to alterations in the protein it encodes. 

Explanation

Molar mass of sodium hydroxide (NaOH) = 23 (Na) + 16 (O) + 1 (H) = 40 g/mol

- For 2 moles: 40 g/mol × 2 = 80 grams

Explanation

A crystal can only have one center of symmetry. 

A center of symmetry is a point within a crystal where, if a line is drawn through that point and extended an equal distance on the other side, it intersects an identical point on the crystal.

Since this is a single, specific point within the crystal, there can only be one center of symmetry per crystal. 

Explanation

 In fructose, the functional group ketone is present on carbon number 2.

This is why fructose is classified as a ketohexose, a six-carbon sugar containing a ketone group. 

Explanation

CH₃MgBr is a Grignard reagent (a source of CH₃⁻ nucleophile).

CH₃O is shorthand for methanal (HCHO) or a methoxy group, depending on context.

Assuming the intended compound is an ester like methyl formate (HCOOCH₃), then:

CH₃MgBr reacts with an ester in two steps:

1. First addition forms a ketone.

2. The second addition gives a tertiary alcohol after hydrolysis.

So, the final product is a tertiary (3°) alcohol.

Explanation

If a vector is given as →A = xi, its magnitude is simply |→A| = √(x²) = x (assuming x ≥ 0).