Which one of the following phenomena cannot be attributed to the refraction of light?

• Twinkling of stars

• Mirage

• Rainbow

• Redshift

The image produced by a concave lens is always

• real

• virtual

• inverted

• enlarged

If the magnitude of vector $\overrightarrow{\mathrm{A}}$ is 10 cm and the direction is North, then what is the magnitude and direction of the vector $-2 \overrightarrow{\mathrm{A}}$?

• 20 cm East

• 20 cm West

• 20 cm North

• 20 cm South

An electric charge q moves with a constant velocity v parallel to the lines of force of a uniform magnetic field B. Force on charge is

• qvB

• qv/8

• Zero

• Bv/q

The pH value of any solution that converts red litmus to blue in color will be

• 1

• 4

• 7

• 10

Rusting of iron is

• Reduction reaction

• Oxidation reaction

• Redox reaction

• Displacement reaction

Petroleum is refined by

• simple distillation

• fractional distillation

• steam distillation

• vacuum distillation

Which one of the following is known as Bayer's Reagent?

• Dilute alkaline solution of potassium permanganate

• Concentrate acidic solution of potassium permanganate

• Acidic solution of potassium permanganate

• Neutral solution of potassium permanganate

The vertical component of Earth's magnetic field is zero at

• magnetic poles

• geographic poles

• everywhere

• magnetic equator

Which is the formula of potash alum?

• (NH₄)₂SO₄ ⋅ Fe(SO₄)₃ ⋅ 24H₂ O

• (NH₄)₂SO₂ ⋅ Al₂(SO₄)₃ ⋅ 24H₂ O

• K₂SO₄ ⋅ Al₂(SO₄)₃ ⋅ 24H₂O

• K₂SO₄ ⋅ Cr₂(SO₄)₃ ⋅ 24H₂O