| 61. | What is the percentage of oxygen in the air approximately? |
A. 21 percent | |
B. 100 percent | |
C. 1 percent | |
D. 78 percent |
| 62. | Who discovered oxygen? |
A. rutherford | |
B. cavendish | |
C. Davy | |
D. Priestley |
| 63. | The most abundant element in the earth’s crust is – |
A. silicone | |
B. calcium | |
C. nitrogen | |
D. oxygen |
| 64. | Which one of the following gases is not a green house gas? |
A. CO₂ | |
B. CH₄ | |
C. NO₂ | |
D. O₂ |
| 65. | Where does the oxygen gas that gives life to humans come from? |
A. Carbon dioxide | |
B. in water | |
C. oxides of metals | |
D. carbonates absorbed from the ground |
| 66. | Which mixture of gases do divers use for breathing? |
A. oxygen and nitrogen | |
B. oxygen and hydrogen | |
C. oxygen and helium | |
D. oxygen and argon |
| 67. | Which of the following is helpful in burning? |
A. oxygen | |
B. hydrogen | |
C. nitrogen | |
D. Carbon dioxide |
| 68. | The oxygen used for artificial respiration in hospitals is a mixture of the following gases: |
A. oxygen and helium | |
B. nitrogen and argon | |
C. oxygen and argon | |
D. oxygen and carbon dioxide |
| 69. | On carrying a stick burning in oxygen gas, it – |
A. she will extinguish | |
B. it extinguishes and the gas starts burning | |
C. it burns fast | |
D. both that and the gas start burning |
| 70. | Which element is found in the largest quantity in the human body? |
A. hydrogen | |
B. nitrogen | |
C. Carbon | |
D. oxygen |