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Read the passage given below and answer the following questions from 1 to 5. Uses of Dihydrogen:

• The largest single use of dihydrogen is in the synthesis of ammonia which is used in the manufacture of nitric acid and nitrogenous
• Dihydrogen is used in the manufacture of vanaspati fat by the hydrogenation of polyunsaturated vegetable oils like soyabean, cotton seeds
• It is used in the manufacture of bulk organic chemicals, particularly
• It is widely used for the manufacture of metal
• It is used for the preparation of hydrogen chloride, a highly useful
• In metallurgical processes, it is used to reduce heavy metal oxides to
• Atomic hydrogen and oxy-hydrogen torches find use for cutting and welding purposes. Atomic hydrogen atoms (produced by dissociation of dihydrogen with the help of an electric arc) are allowed to recombine on the surface to be welded to generate the temperature of 4000
• It is used as a rocket fuel in space
• Dihydrogen is used in fuel cells for generating electrical energy. It has many advantages over the conventional fossil fuels and electric It does not produce any pollution and releases greater energy per unit mass of fuel in comparison to gasoline and other fuels.

Dihydrogen, under certain reaction conditions, combines with almost all elements, except noble gases, to form binary compounds, called hydrides. If ‘E’ is the symbol of an element then hydride can be expressed as EHx $($e.g., Mg $H_2)$ or EmHn $($e.g.,$B_2H_6)$. The hydrides are classified into three categories:

• Ionic or saline or saltlike hydrides
• Covalent or molecular hydrides
• Metallic or non-stoichiometric hydrides

Ionic or Saline Hydrides are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character. However, significant covalent character is found in the lighter metal hydrides such as LiH, $BeH_2$ and $MgH_2$. In fact Be $H_2$ and Mg $H_2$ are polymeric in structure. The ionic hydrides are crystalline, non-volatile and non- conducting in solid state. However, their melts conduct electricity and on electrolysis liberate dihydrogen gas at anode, which confirms the existence of $H^{–} ion$. Covalent or Molecular Hydride Dihydrogen forms molecular compounds with most of the p-block elements. Most familiar examples are $CH_4, NH_3, H_2O$ and $HF.$ For convenience hydrogen compounds of non- metals have also been considered as hydrides. Being covalent, they are volatile compounds. Molecular hydrides are further classified according to the relative numbers of electrons and bonds in their Lewis structure into:

• electron-deficient,
• electron-precise, and
• electron-rich

An electron-deficient hydride, as the name suggests, has too few electrons for writing its conventional Lewis structure. Diborane $(B_2H_6)$ is an example. In fact all elements of group 13 will form electron-deficient compounds. They act as Lewis acids i.e., electron acceptors. Electron-precise compounds have the required number of electrons to write their conventional Lewis structures. All elements of group 14 form such compounds (e.g., $CH_4$) which are tetrahedral in geometry. Electron-rich hydrides have excess electrons which are present as lone pairs. Elements of group 15-17 form such compounds. (NH3 has 1 - lone pair, $H_2O – 2$ and $HF –3$ lone pairs). What do you expect from the behaviour of such compounds ? They will behave as Lewis bases i.e., electron donors. The presence of lone pairs on highly electronegative atoms like N, O and F in hydrides results in hydrogen bond formation between the molecules. This leads to the association of molecules. Metallic or Non-stoichiometric (or Interstitial ) Hydrides are formed by many d- block and f-block elements. However, the metals of group 7, 8 and 9 do not form hydride. Even from group 6, only chromium forms CrH. These hydrides conduct heat and electricity though not as efficiently as their parent metals do. Unlike saline hydrides, they are almost always non- stoichiometric, being deficient in hydrogen. For example, $La H_{2.87}, Yb H_{2.55}, TiH1_{.5–1.8}, ZrH_{1.3–1.75}$, etc. In such hydrides, the law of constant composition does not hold good. Earlier it was thought that in these hydrides, hydrogen occupies interstices in the metal lattice producing distortion without any change in its type. Consequently, they were termed as interstitial hydrides. However, recent studies have shown that except for hydrides of Ni, Pd, Ce and Ac, other hydrides of this class have lattice different from that of the parent metal. The property of absorption of hydrogen on transition metals is widely used in catalytic reduction / hydrogenation reactions for the preparation of large number of compounds. Some of the metals (e.g., Pd, Pt) can accommodate a very large volume of hydrogen and, therefore, can be used as its storage media. This property has high potential for hydrogen storage and as a source of energy. A major part of all living organisms is made up of water. Human body has about 65% and some plants have as much as 95% water. It is a crucial compound for the survival of all life forms. It is a solvent of great importance. The distribution of water over the earth’s surface is not uniform.​​​​​​​

1. Dihydrogen, under certain reaction conditions, combines with almost all elements, except …

1. Noble gases
2. Halogens
3. Alkali metals
4. Alkaline earth metal

2. Covalent or Molecular Hydride Dihydrogen forms molecular compounds with most of the p-block elements. Most familiar example is:

1. $CH_4$
2. $NH_3$
3. $H_2O$
4. All the above

3. All elements of group 14 form such compounds have … geometry.

1. pyramidal
2. tetrahedral
3. bilateral
4. spherical

4. From group 6, only … forms hydride.

1. molybdenum
2. tungsten
3. chromium
4. seaborgium

5. Which of the following hydride is/ are deficient in hydrogen.

1. $La H_2._{87}$
2. $Yb H_2._{55}$
3. TiH5–1.8
4. All of above