100+ Chemistry Questions and Answers for Competitive Exams - 2

Question: 6

Why gypsum added to cement?

The addition of gypsum to cement, acts as a retardant for setting of cement. i.e. it slows down the rate of setting of cement.

Question: 7

What is meant by efflorescence?

The process of losing water to crystallization from a hydrated salt when kept exposed to air for a long time is called as efflorescence.

Question: 8

What is valence shell?

The outer most shell of an atom is called valence shell.

The electrons present in the valence shell are called valence electrons.

Question: 9

What is radiocarbon dating?

The age of fossils and rocks can be determined using radioactive isotope of carbon since it has half life of 5730 years.

This is called radio carbon dating.

Question: 10

Name the instruments used to detect radioactive rays?

Radioactive rays can be detected by using

(i). Electrometer

(ii). Cloud chamber

(iii). Geiger Muller counter

(iv). Semiconductor circuits