216: Which of the following professional (s) are more likely to run the risk of a permanent change in their cell's DNA ?
I. Researchers using carbon-14 isotope
II. X-ray technician
III. Coal miner
IV. Dyer and Painter
Select the correct answer by using the codes given below :
(a) II alone
(b) I, II and III
(c) I, II and IV
(d) I, III and IV
Explanation:
X-rays can damage the cell and tissues and finally cause mutation, even excesive dose burns the cell and leads to cancer. Researchers using C-14 isotopes and coal miners too expose to the radiations released in less concentrations continuously will lead to mutation in their cell's DNA.
217: Another name of Vitamin C is:
(a) Folic acid
(b) Ascorbic acid
(c) Niacin
(d) Acetic acid
218: Which one of the following pairs of metals constitutes the lightest metal and the heaviest metal, respectively?
(a) Lithium and mercury
(b) Lithium and osmium
(c) Aluminium and osmium
(d) Aluminium and mercury
Explanation:
The lightest metal in the periodic table is lithium (Li) with atomic number 3. However, the metal with the highest strength to weight ratio is titanium (Ti). Lithium metal is extremely soft (and highly reactive) and so is unusable for most applications, but one atom of Li weighs 1/7th of an atom of Ti.
Osmium is a hard metallic element which has the greatest density of all known elements. It is twice as heavy as lead, and has a specific gravity of 22.59. (The specific gravity of lead is 11.35; gold is 19.32; and platinum is 21.45.) Osmium has an atomic weight of 190.2 and its atomic number is 76.
219: Which one of the following is not an essential micronutrient for plants ?
(a) Boron
(b) Zinc
(c) Sodium
(d) Copper
Explanation:
Micro nutrients or trace elements are essential mineral elements which are required in small quantities for plant growth and development . They are Fe, Mn, B, Cu, Zn Mo and CL. Recently 'Nickel (Ni)' added to the list of micronutrients. Sodium (Na) is not essential nutrient as it is not required in all the plants for their growth and development except in halophytes.
220: Very small-time intervals are accurately measured by the:
(a) Pulsars
(b) White dwarfs
(c) Atomic clocks
(d) Quartz clocks