Answer:
B. ADDITION OF TWO GROUPS ACROSS A DOUBLE BOND
Explanation:
Addition reaction of alkenes involves the conversion of the double bond in alkenes Inyo single bonds by the addition of two groups of atoms or radicals.
During this addition reaction, two substances, an unsaturated compound(e.g. ethane) and an attacking reagent (hydrogen, halogens, hydrogen halides, chlorine and bromine water) combines to form a single new compound without forming any other products. So a saturated product or one in which is an increase in degree of saturation is formed.
Answer:
It is a pure substance. Magnesium is an element.
Answer: 873 kJ of energy will be required to break two moles of hydrogen gas.

Above chemical equation shows that two moles of hydrogen gas is reacting with one mole of oxygen gas to give two mole of water molecule.
Bond energy of H-H = 436kJ
According to reaction we have two moles hydrogen,so energy required to break the
H-H bond in two moles of hydrogen gas will be:

= 872kJ
872kJ of energy will be required to break H-H bond in two moles of hydrogen gas.
Answer: Objects with like charge repel each other.
Answer:
Potassium
Explanation:
The atom with the largest atomic radius is potassium from the given list.
The atomic radius is taken as half of the inter-nuclear distance between two covalently bonded atoms of non-metallic elements or half of the distance between nuclei in the solid metal state.
Across a period in the periodic table, atomic radii decreases progressively from left to right.
This is due to the progressive increase in the nuclear charge without an attendant increase in the number of electronic shells.