S – S bond is present in

1. ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7$

2. ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$

3. ${\mathrm{H}}_2{\mathrm{SO}}_5$

4. ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6$

Which is incorrectly given according to the order indicated?

The correct order of acidic strength of oxyacids of phosphorous is

Which is mismatched with respect to the shapes of the compounds given?

On addition of conc. H₂SO₄ to a chloride salt, colourless fumes are evolved but in case of iodide salt, violet fumes come out. This is because

1. H₂SO₄ reduces HI to I₂

2. HI is of violet colour

3. HI gets oxidised to I₂

4. HI changes to HIO₃

Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy?

1. HF

2. HCl

3. HBr

4. HI

Bond dissociation enthalpy of E—H (E = element) bonds is given below. Which of the compounds will act as strongest reducing agent?

Compound                    $N{H}_3$              $P{H}_3$                 $As{H}_3$                 $Sb{H}_3$

${∆}_{diss}(E-H)/kJ mo{l}^{-1}$     389             322                  297                    255

1. $N{H}_3$

2. $P{H}_3$

3. $As{H}_3$

4. $Sb{H}_3$

On heating with concentrated NaOH solution in an inert atmosphere of CO₂, white phosphorus gives a gas.
Incorrect statements among the following about the gas is: 

Which of the following acids forms three series of salts?

1. H₃PO₂

2. H₃BO₃

3. H₃PO₄

4. H₃PO₃

Which of the following elements does not show allotropy?

1. Nitrogen

2. Bismuth

3. Antimony

4. Arsenic