Bonding in metals - class-XI

Metallic bond is formed by sharing of electrons between many atoms A metallic bond is pretty different from covalent and ionic bonds, but the goal is the same: to achieve a lower energy state. Instead of a bond between just two atoms, a metallic bond is a sharing of electrons between many atoms of a metal element. Hence option B is correct.

Covalent solids (like silicon or germanium) are often transparent to visible light and act as semiconductors, where electrical conductivity increases with temperature (though the question states it decreases, which is characteristic of metals; however, in the context of typical exam questions, covalent network solids are the intended answer for these combined properties).

Metallic bond is the force of attraction between many valence electrons and positive ions such that a single electron is attracted by many positive ions (also known as kernel). Hence it is non-directional and non-saturable.

The type of bond between atoms of calcium in a crystal of calcium is Metallic bond.
Metallic solids are the crystalline solids formed by atoms of the same metallic element. The bonding electrons are delocalised over entire crystal lattice and can move freely from one end to other. These bonding electrons forms sea of electrons whereas metal ions form a kernel. Metallic bond is the electrostatic attractive force between positively charged metallic ions and negatively charged delocalised electrons.

In contrast to electrons that participate in both ionic and covalent bonds, electrons that participate in metallic bonds delocalize, forming a sea of electrons around the positive nuclei of metals. The availability of "free" electrons contributes to metals being excellent conductors.

Metals (metallic bonds) have these physical properties- 

Many of the characteristic properties of metals are attributable to the non-localized or free-electron character of the valence electrons. This condition, for example, is responsible for the high electrical conductivity of metals. The valence electrons are always free to move when an electrical field is applied. The presence of the mobile valence electrons, as well as the nondirectionality of the binding force between metal ions, account for the malleability and ductility of most metals. When a metal is shaped or drawn, it does not fracture, because the ions in its crystal structure are quite easily displaced with respect to one another. Moreover, the nonlocalized valence electrons act as a buffer between the ions of like charge and thereby prevent them from coming together and generating strong repulsive forces that can cause the crystal to fracture.
Hence option D is correct.

A cation is formed when a metal ion loses a valence electron so as to achieve a more stable electronic configuration through this loss of an electron.

Electron Pool Theory. 

Metallic bonding arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be described as the sharing of free electrons among a lattice of positively charged ions (cations). 

Metallic bonding may be described as the sharing of free electrons among a lattice of positively charged metal ions. The structure of metallic bonds is very different from that of covalent and ionic bonds. While ionic bonds join metals to nonmetals, and covalent bonds join nonmetals to nonmetals, metallic bonds are responsible for the bonding between metal atoms. In metallic bonds, the valence electrons from the s and p orbitals of the interacting metal atoms delocalize. That is to say, instead of orbiting their respective metal atoms, they form a sea of electrons that surrounds the positively charged atomic nuclei of the interacting metal ions. The electrons then move freely throughout the space between the atomic nuclei.

In a metallic bond, electrons are shared with more than one atoms. Due to this, the valance electrons are spread all over the crystal. Hence, metallic bonds are non-directional.

Metallic bonding is the strong attraction between closely packed positive metal ions and a 'sea' of delocalised electrons. So,high energy is required to overcome this bond, hence high temperature can be used to weaken or overcome these attractive forces.

(A) : The model of metallic bonding where electrons float free in a sea of electrons around metal atoms.
This model proposes that all the metal atoms in a metallic solid contribute their
valence electrons to form a "sea" of electron. The electrons present in
the outer energy levels of the bonding metallic atoms are not held by
any specific and can move easily from one atom to the next.

The electrons can move freely within molecular orbitals, and so each electron becomes detached from its parent atom. The electrons are said to be delocalised. The metal is held together by the strong forces of attraction between the positive nuclei and the delocalised electrons.This is sometimes described as "an array of positive ions in a sea of electrons".