Metals And Non Metals

Gold (Au) is one of the least reactive metals. It does not corrode easily, does not react with air or water under normal conditions, and is found in nature in its elemental form. In contrast:
Potassium (K) is extremely reactive, especially with water.
Magnesium (Mg) is also reactive, though less so than potassium.
Iron (Fe) reacts with moisture and oxygen, forming rust.

The correct option is (B): Au

Correct answer: gangue

Explanation:
The unwanted impurities like soil, sand, and rock that are mixed with the ore are known as gangue. During the process of ore purification, these are removed using physical or chemical methods.

Correct answer: it is less reactive

Explanation:
Gold is a noble metal and lies at the bottom of the reactivity series. It does not easily react with air, water, or acids. Due to its low reactivity, gold is found in the earth's crust in its native (free) state, rather than as a compound.

Valency is the ability of an atom to bond with other atoms, which is determined by the number of electrons in its outermost shell. Non-metals, which are typically found on the right side of the periodic table, tend to gain electrons to achieve a stable electron configuration, often aiming for a full outer shell, similar to that of noble gases.

In other words, the valency of a non-metal element corresponds to the number of electrons it needs to gain to complete its outer shell. This is why the number of electrons gained by a non-metal element is equal to its valency. Among the options provided, 'valency' is the correct answer.

The hardest substance in the human body is tooth enamel. Tooth enamel is primarily made up of a mineral known as hydroxyapatite, which is a crystalline structure composed of calcium phosphate. Therefore, among the given options, the correct answer is calcium phosphate.
Tooth enamel's strength and hardness come from its dense mineral content, with calcium phosphate being the key component. None of the other options (calcium sulphate, calcium chloride, magnesium sulphate) form substances as hard as tooth enamel in the human body.