An cation A3+ has 18 electrons. Write the atomic number of A.a)15b)24c)12d)21Correct answer is option 'D'. Can you explain this answer?

Question

Answer

3+ charge means no of electrons will be 3 less than no. of protons. So no. of protons will be 21. So atomic no. is 21.

Answer

Electron = atomic number +- electron   solutions 18=A -  3 = 21 ( sign opposite just A )

Answer

The cations are those ions which donate their electrons. If the cation is having +3 charge and now have 18 electrons, then its atomic number=18+3 =21 This shows that option 'd' is correct.

Answer

**Explanation:**

To determine the atomic number of A, we need to know the number of electrons it has.

Given that A3 has 18 electrons, we can use the electron configuration to find the atomic number of A.

**Step 1: Determine the electron configuration of A3**

The electron configuration of an element shows the arrangement of electrons in its atomic orbitals.

Since A3 has 18 electrons, we need to fill the orbitals according to the Aufbau principle.

The Aufbau principle states that electrons fill the lowest energy orbitals first before filling higher energy orbitals.

The electron configuration of A3 can be written as:

1s² 2s² 2p⁶ 3s² 3p⁶

**Step 2: Determine the highest energy level filled**

The highest energy level filled in the electron configuration is the third energy level.

Therefore, the atomic number of A is the number of protons in the nucleus, which is equal to the number of electrons.

Since the highest energy level filled is the third energy level, the atomic number of A is the number of electrons in the first three energy levels.

**Step 3: Calculate the atomic number**

To calculate the atomic number, we add up the number of electrons in the first three energy levels:

1s² + 2s² + 2p⁶ + 3s² + 3p⁶ = 18

Therefore, the atomic number of A is 18.

**Step 4: Determine the correct option**

Now we need to compare the calculated atomic number (18) with the options given.

a) 15 - Incorrect, as the atomic number of A is not 15.

b) 24 - Incorrect, as the atomic number of A is not 24.

c) 12 - Incorrect, as the atomic number of A is not 12.

d) 21 - Correct, as the atomic number of A is indeed 18.

Therefore, the correct answer is option D) 21.

Answer

Answer d is correct bcz when z=21 then A3+have 18 electron . It is bcz A remove 3 electrons from its atomic no. tthen it have 18 electron remain

Answer

Atomic no. =no. of proton , so here no. of proton =18+3=21 bcoz, on releasing electron positive charge increases......

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