21.

The electronic configuration is 1s² 2s² 2p⁵ 3s¹  shows

• ground state of fluorine atom

• excited state of fluorine atom

• excited state of neon atom

• excited state of ion O₂

Assertion: Relative strength of acids can be known by knowing the value of dissociation constant.

Reason : It gives the value of H dissolved in solution.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Assertion : CHCl₃ and CH₃OH are miscible.

Reason : One of them is polar.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Assertion : B₂H₆, Si₂H₆, are said to have similar structure.

Reason : They have same number of $\mathrm{\sigma }$ and $\mathrm{\pi }$ bonds.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Assertion : Hydrogen nuclei combines to form helium nuclei then energy is released.

Reason: Binding energy/nucleon of He is greater than hydrogen.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Assertion : Water is used as a moderator in nuclear reactor.

Reason : Moderator is a light substance that absorb neutrons.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Assertion : Ionisation potential of B (atomic no.5) is less than Be (atomic no. 4).

Reason : The first electron released from Be is of p-orbital but that from B is of s-orbital.

• If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

• If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• If Assertion is true but Reason is false.

• If Assertion is false but Reason is true.

Which of the following is aromatic?

Which ofthe following is most stable carbocation?

• CH₃⁺

• CH₃CH₂$\stackrel{+}{\mathrm{C}}$H₂

• CH₃$$\begin{gathered} \stackrel{ \\ +}{\mathrm{C}} \end{gathered}$$HCH₃

• CH₃-(CH₃)$\stackrel{+}{\mathrm{C}}$-CH₃

Which of the following has highest hydration energy?

• MgCl₂

• CaCl₂

• BaCl₂

• SrCl₂