Uranium, Thorium and Polonium are radioactive elements which do not have stable naturally occurring isotope. Aluminium is a silvery white, soft, ductile metal. It is the third most abundant element (after oxygen and silicon), and the most abundant metal in the Earth’s crust.

Correct Option: C

Uranium, Thorium and Polonium are radioactive elements which do not have stable naturally occurring isotope. Aluminium is a silvery white, soft, ductile metal. It is the third most abundant element (after oxygen and silicon), and the most abundant metal in the Earth’s crust.

Noble gas refers to any of the seven chemical elements that make up Group VIIIa of the periodic table. The elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and element 118 (temporarily named ununoctium [Uuo]).

Correct Option: D

Noble gas refers to any of the seven chemical elements that make up Group VIIIa of the periodic table. The elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and element 118 (temporarily named ununoctium [Uuo]).

Mercury and DDT are two persistent toxic materials that accumulate in the food chain and damage the organisms in it. DDT is an insecticide that can pass up the food chain from insects to small birds, and then from the small birds to birds of prey. It is now banned because of this.

Correct Option: A

Mercury and DDT are two persistent toxic materials that accumulate in the food chain and damage the organisms in it. DDT is an insecticide that can pass up the food chain from insects to small birds, and then from the small birds to birds of prey. It is now banned because of this.

Cast Iron is a hard, brittle, nonmalleable iron-carbon alloy, cast into shape, containing 2 to 4.5 percent carbon. Steels contain less than 2% and usually less than 1% carbon, while all cast irons contain more than 2% carbon. Most steel contains less than 0.35 percent carbon. Wrought iron is an iron alloy with very low carbon (0.04 to 0.08%) content.

Correct Option: A

Cast Iron is a hard, brittle, nonmalleable iron-carbon alloy, cast into shape, containing 2 to 4.5 percent carbon. Steels contain less than 2% and usually less than 1% carbon, while all cast irons contain more than 2% carbon. Most steel contains less than 0.35 percent carbon. Wrought iron is an iron alloy with very low carbon (0.04 to 0.08%) content.

The most important buffer for maintaining acidbase balance in the blood is the carbonic-acid-bicarbonate buffer. Three different buffer systems exist in blood, the bicarbonate buffer and the phosphate buffer are composed of "simple" chemicals. In addition the carbonyl groups (-COOH) and the amide group (NH₂) present on proteins allow some of these to act as buffers.
H₂CO₃ + H₂O ↔ HCO₃ ^- +H₃O⁺

H₂PO₄^- +H₂O ↔ HPO₄H₃O 2⁺

Correct Option: D

The most important buffer for maintaining acidbase balance in the blood is the carbonic-acid-bicarbonate buffer. Three different buffer systems exist in blood, the bicarbonate buffer and the phosphate buffer are composed of "simple" chemicals. In addition the carbonyl groups (-COOH) and the amide group (NH₂) present on proteins allow some of these to act as buffers.
H₂CO₃ + H₂O ↔ HCO₃ ^- +H₃O⁺

H₂PO₄^- +H₂O ↔ HPO₄H₃O 2⁺