H⁺ ions always get associated with other atoms or molecules due to -

1.	Ionisation enthalpy of hydrogen resembles that of alkali metals
2.	Its reactivity is similar to halogens
3.	It resembles both alkali metals and halogens
4.	Loss of an electron from hydrogen atom results in a nucleus of very small size as compared to other atoms or ions. Due to small size it cannot exist free

Some statements about water are given below:
 

Which of the above statements are correct?

1. (a), (b), and (c)

2. (b) and (c)

3. (a) and (c)

4. (a) and (b)

The correct order of increasing reducing nature is -

1. NaH > H₂O < MgH₂

_{2. ${\mathrm{H}}_2\mathrm{O}$ > ${\mathrm{MgH}}_2$> NaH}

_{3. ${\mathrm{H}}_2\mathrm{O}$< ${\mathrm{MgH}}_2$ < NaH}

_{4. ${\mathrm{H}}_2\mathrm{O}$ $\simeq$ ${\mathrm{MgH}}_2$ < NaH}

The correct order of increasing electrical conductance is -
1. BeH₂ > CaH₂ > TiH₂
2. BeH₂ < CaH₂ > TiH₂
3. TiH₂ < BeH₂ < CaH₂
4. BeH₂ < CaH₂ < TiH₂

Structures of  and ${}^{}\mathrm{O\; is/are}$

$$ {}^{}{}^{}$$ {}^{}\mathrm{O has\; a\; bent\; structure\; .}$$

$$ \mathrm{2.}$$

Industrial preparation of H₂​O₂ is-

1. By the action of dilute sulphuric acid: BaO₂​.8H_2​O(s) + H₂​SO₄​(aq) → BaSO₄​(s) + H₂​O₂​(aq) + 8H₂​O(l)

2. By the action of carbon dioxide: BaO₂​ + H₂​O + CO₂​ → BaCO₃ ​+ H₂​O₂​

3. By the action of phosphoric acid: 3BaO₂​ + 2H₃​PO₄​ → Ba₃​(PO₄​)₂​ + 3H₂O₂​

4. ${\mathrm{H}}_2{\mathrm{O}}_2 + 2 \mathrm{ethylanthraquinol} \underset{{\mathrm{H}}_2/\mathrm{Pd}}{\overset{{\mathrm{O}}_2 \left(\mathrm{air}\right)}{\rightleftharpoons }} {\mathrm{H}}_2{\mathrm{O}}_2 + \mathrm{Oxidised} \mathrm{Products}$

Physical properties in which D₂O differs from H₂O is/are:

1. solubility of salts in heavy water is less than in ordinary water

2. all physical constants of D₂O are higher than H₂O. 

3. heavy water is almost 11% denser than light (normal) water.

4. all of the above.

Atomic hydrogen combines with almost all elements but molecular hydrogen does not because

1. Atomic hydrogen is highly unstable molecular, hydrogen is almost inert at room temperature.

2. Atomic hydrogen is highly inert, molecular hydrogen is almost unstable at room temperature.

3. Atomic hydrogen and molecular hydrogen are unstable.

4. Atomic hydrogen and molecular hydrogen are inert.

Choose reactions to explain the amphoteric nature of water.

$1) {\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{NH}}_3(\mathrm{aq})\to {\mathrm{OH}}^{-}(\mathrm{aq})+{\mathrm{NH}}_4^{+}(\mathrm{aq})$
$2) {\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{H}}_2\mathrm{S}(\mathrm{aq})\to {\mathrm{H}}_3{\mathrm{O}}^{+}(\mathrm{aq})+{\mathrm{HS}}^{-}(\mathrm{aq})$
$3) \mathrm{a} \& \mathrm{b}$
$4) \mathrm{none}$

The pair that on reaction will not evolve $H_2$ gas is  

1.  Copper and HCl (aqueous)
2.  Iron and steam
3.  Iron and $H_{2}S{O}_4$ (aqueous)
4.  Sodium and ethyl alcohol