Why is benzene extra ordinarily stable though it contains three double bonds?

Which of the following contains a double bond?

Which of the following does not contain a double bond?

Assertion: Benzene does not give electrophilic substition reactions. Reason: Benzene ring has extraordinarily stability because of delocalisation of six pi -electrons of three double bonds.

Which amongst the following contains double covalent bond?

A hydrocarbon has the formula C_(3)H_(4) . To find out whether it contains two double bond or a triple bond, the following test is preffered:

Explain (a )Which d-orbital in involved in (i) sp^(3) d hybridisation (ii) sp^(3) d^(2) hybridisation (iii) dsp^(2) hybridisation (iv) sp^(3)d^(3) hybridisation (b) Why H_(2)O is liquid while H_(2)S is gas (c ) Why KHF_(2) exists but KHCI_(2) does not (d) Benzene ring contains alternate single and double bonds yet all the C-C bonds are of equal lenght why (e) Out of P-F,CI-F,S-F and F-F bonds, which bond is the least ionic? .