Grade 8 first term

The halogen that can replace all the halogens in its salt compound is....................................

• chlorine

• bromine

• fluorine

• iodine

Alkali metals are kept under kerosone except..............................is kept under paraffin oil.

• sodium

• lithium

• rubidium

• potassium

Who discovered the 7 energy levels?

• Mendeleev

• Mosely

• Bohr

• Rutherford

When you put glass bottle filled with water, it explodes. G.R

• Because mass increases, so density decreases.

• Because density decreases and volume decreases

• As temp becomes less than 4 Celsius, crystals of ice are formed which increases the mass

• As temp becomes less than 4 Celsius, crystals of ice are formed which increases the volume

The temperature increases in the stratosphere due to.....................................until it reaches....................

• oxygen, 0 degree Celsius

• ozone, -60 degree Celsius

• weather changes, 25 degree Celsius

• ozone, 0 degree Celsius

Group 1A is called..................................while group zero is...............................

• alkali metals and noble gases
• noble gases and transition metals
• halogens and transition metals
• alkali metals and halogens

If the temperature at the sea level is 20 degree Celsius, find the temperature of a top of mountain of a height of 5000 m.

• -12.5 degree Celsius

• -32480 degree Celsius

• 6.5 degree Celsius
• 0 degree Celsius

When magnesium react with dilute HCl, it produces..............................which is..............................

• MgCl, a salt

• MgO, a base

• MgH2, an acid

• MgCl2, a salt

Silicon is used in electronic devices such as computer because it is................................

• Due to low boiling point of -196 degree Celsius

• a source of renewable energy
• a semiconductor material that conducts electricity while changing temperature

• a good conductor of heat

Sodium fires cannot be extinguished using water. (Give reasons)

(Write the equation)

• Because water is good conductor of heat

  Na+O2=Na2O

• Because water reacts with sodium producing hydrogen that burns with pop sound.

  na+h2o=naoh+h2

• Because water reacts with sodium producing hydrogen that burns with pop sound.

  2Na+2H2O=2NaOH+H2

• Because water is good conductor of heat

  Na+HCl=NaCl+H2