question_answer

Directions: (Q. 16 to 20)

Case IV: Read the passage given below and answer the following questions.

Most important crystal lattices are the simple cubic, body centred cubic and face centred cubic.

In simple cubic lattice, all the atoms are present at all the corners of the cube. In body-centred cubic lattice, atoms are present at all the corners and at the body-centre. In face-centred cubic lattice, atoms are present at the corners and at the centers of all six faces.

In the formation of crystals, the constituent particles get closely packed together. The closely packed arrangement is that in which maximum available space is occupied leaving minimum vacant space. The most efficient close packing, can be achieved in two ways, one which is called hexagonal close packing (hcp) and the other, cubic close packing (ccp or fcc).

In the following questions (Q. No. 16-20), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

Assertion: Face centred cubic cell has atoms per unit cell.

Reason: In fcc unit cell, there are 8 atoms at the corners and 6 atoms at face centres.

A) Assertion and reason both are correct statements and reason is correct explanation for assertion.

B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

C) Assertion is correct statement but reason is wrong statement.

D) Assertion is wrong statement but reason is correct statement.