51.

Invar, an alloy of Fe and Ni is used in watches and meter scale. Its characteristic property is

• small coefficient of expansion

• resistance of corrosion

• hardness and elasticity

• magnetic nature

An alloy of Pb and Sn in equal proportion is called:

• solder

• constantan

• gun metal

• type metal

A compound with cubic structure is made of elements A and B. A atoms are at the corners of the cube and B atoms are at the face centres. The simplest formula of the compound is :

• A₅B

• AB₃

• AB

• AB₆

Which of the following unit cell having maximum number of atoms ?

• BCC

• HCP

• FCC

• Cubic

Silicon is

• semiconductor

• insulator

• conductor

• None of these

If the mass defect of a nuclide is 3.32 x 10^-26g, its binding energy is ......... MeV

• 9.31

• 18.62

• 27.93

• 37.24

AB is an ionic solid. The ionic radii of A⁺ and B^- are respectively r_c and r_a. Lattice energy of AB is proportional to :

• $\frac{{\mathrm{r}}_{\mathrm{c}}}{{\mathrm{r}}_{\mathrm{a}}}$

• (r_c + r_a)

• $\frac{{\mathrm{r}}_{\mathrm{a}}}{{\mathrm{r}}_{\mathrm{c}}}$

• $\frac{1}{\left({\mathrm{r}}_{\mathrm{c}} + {\mathrm{r}}_{\mathrm{a}}\right)}$

If the mass defect of ₅B¹¹ is 0.081 u, its average binding energy (in MeV) is

• 8.60

• 6.85

• 5.60

• 5.86

Which of the following statements is correct ?

• Silicon doped with boron is an n-type semiconductor

• Silicon doped with arsenic is a p-type semiconductor

• Metals are good conductors of electricity

• Electrical conductivity of semiconductors decreases with increasing temperature

Assertion (A): White tin is an example of tetragonal system.
Reasoning (R): For a tetragonal system a= b = c and  α = β = γ ≠ 90°. The correct answer is

• (A) and (R) are true and (R) is the correct explanation of (A).

• Both (A) and (R) are true and (R) is not the correct explanation of (A).

• (A) is true but (R) is not true.

• (A) is not true but (R) is true.