Which of the following is not a synthetic abrasive?

Which of the following is also known as residual asphalt?

Which of the following is not a natural abrasive?

Nitrocellulose glues are prepared from _____

Coal gas is obtained by thermal decomposition of coal in the presence of air at low temperature.

Which of the following statements about liquid lubricants is false?

The ratio of the percentage of alumina to that of oxide of iron in the cement should not be less than ____

Tensile strength of rubber belts is about ___