81.

Which of the following metallic oxide exhibit amphoteric nature?

• CaO

• Al₂O₃

• Na₂O

• BaO

Borax bead test of Cr (chromium) is :

• green

• blue

• violet

• brown

Graphite is a soft solid lubricant extremely difficult to melt. The reason for this anomalous behaviour is that, graphite

• is a non-crystalline substance

• is an allotropic form of diamond

• has molecules of variable molecular masses like polymers

• has carbon atoms arranged in large plates of rings of strongly bound carbon atoms with weak interplate bonds

The structure of diborane (B₂H₆) contains

• four 2C-2e^- bonds and four 3C-2e^- bonds

• two 2C-2e^- bonds and two 3C-3e^- bonds

• two 2C-2e^- bonds and four 3C-2e^- bonds

• four 2C-2e^- bonds and two 3C-2e^- bonds

Dry ice is:

• solid SO₂

• Solid NH₃

• Solid O₂

• Solid CO₂

Crystalline form of silica is called :

• crystalline silicon

• quartz

• rock

• talc

The elements commonly used for making transistors are :

• C and Si

• Ga and In

• P and As

• Si and Ge

Buckminster fullerene is :

• pure graphite

• C-60

• diamond

• C-90

White lead is

• PbCO₃PbO

• PbCO₃

• Pb(OH)₂.2PbCO₃

• PbSO₄.PbO

In silica (SiO₂), each silicon atom is bonded to

• two oxygen atoms

• four oxygen atoms

• one silicon and two oxygen atoms

• one silicon and four oxygen atoms