Mode of occurrence of elements in nature - class-X

Aluminium is the most abundant metal in the earth's crust. The second most abundant metal in the earth is iron and third one is calcium.

Some metals are found in earth's crust in the free state. Some are found in the form of their compounds. The metals at the bottom of activity series are least reactive.

The oxide ore of zinc is known as zincite.

Metals found at the top of the reactivity series are never found in free-state as they are very reactive, e.g. K, Na, Ca, Mg and Al, etc.

Rubies are crystalline forms of aluminium oxide, which are red in colour due to the presence of chromium as an impurity. 

The carbonate and silicate ore of zinc is called as calamine and hemimorphite respectively.

 Carbonate ores are Magnesite $(MgCO _3)$, Dolomite $(CaCO _3MgCO _3)$, Calamine $(ZnCO _3)$, Malachite $(CuCO _3.Cu (OH) _2)$, Siderite $(FeCO _3)$, and Limestone $(CaCO _3)$.

The chief ore of aluminium is bauxite $(Al _2O _3.2H _2O)$. Corundum $(Al _2O _3)$ and Cryolite $(Na _3AlF _6)$ are also aluminium ores. Epsomite is a hydrous magnesium sulfate ore with formula $MgSO _4·7H _2O$.

Sulphate ores are  Gypsum $(CaSO _4.2H _2O)$, Epsom Salt $(MgSO _4.7H _2O)$, Barytes $(BaSO _4)$ and Anglesite $(PbSO _4)$.

Cinnabar is the most common  and is the chief ore of mercury with formula $HgS$.

Copper(Cu), gold(Au) and silver(Ag) exist in their native state in the earth's crust, and are collectively called coinage metals.

Given statement is false. Very few elements occur in the free state - example: gold, platinum etc. The rest of the elements are found in the combined state as compounds such as carbonates,sulphides, oxides etc.

Gold and Silver occur in native forms since they are non reactive metal.

In general, elements located in the left two-thirds of the periodic table are metals, and the non-metals are on the right side of the table. 

In the metal reactivity series, metals are arranged in descending order of reactivity, with the most reactive metals at the top.

Stainless steel is an alloy of iron, chromium, and carbon, where carbon is a non-metal. Brass, bronze, and solder are alloys consisting entirely of metallic elements such as copper, zinc, tin, and lead.

Very few metals exist in the free or native state. Only metals like gold, platinum and mercury are occasionally found in the free state, i.e., in the pure form.

Hydrogen is more plentiful than any other element making up about 3/4th the mass of the universe. Helium is second making up almost all of the remaining $25%$. Oxygen is third most abundant element of universe. On earth, oxygen is the most common element making up about $47%$ of earth's mass.

1) Chlorophyll contains a magnesium ion, encased in a large ring structure known as a chlorine.

 2) The chlorine ring is a heterocyclic compound derived from pyrrole. 

Calcium occurs as carbonate in limestone $(CaCO _{3})$ and as flouride in flourspar $(CaF _{2})$.

Sodium occurs as chloride in rock salt, $(NaCl)$ and calcium occurs as fluoride in flourspar $(CaF _{2})$.

Copper occurs as an oxide ore as cuprite $(Cu _{2}O)$ and as sulphide ore as copper glance $(Cu _{2}S)$.

Anglesite, baryte and gypsum all are ores of sulphate.

The most abundant elements in the earth crust is Oxygen as many compounds are in form of their oxides.

The most abundant metal in the earth's crust is $Al$.

Copper and silver are two metals which occur in free as well as combined state as sulphide, oxide or halide ores. 

Iron is mainly extracted from its oxide ores such as haematite and magnetite. The iron extracted from these ores is mostly used in the manufacture of steel an alloy of iron. Iron is also an essential element found in biological systems.

Minerals that have a relatively high concentration of metal and can be extracted in an easy and cost-effective process are called ores.

The halide ore of sodium is called as rock salt or common salt.

Silver glance or argentite is the sulphide ore of silver.

The metals at the bottom of the activity series are the least reactive. They are often found in a free state. For example, gold, silver, platinum and copper are found in the free state. Copper and silver are also found in the combined state as their sulphide or oxide ores. The metals at the top of the activity series $(K, Na, Ca, Mg$ and $Al)$ are so reactive that they are never found in nature as free elements. The metals in the middle of the activity series $ (Zn, Fe, Pb, etc.)$ are moderately reactive. They are found in the earth’s crust mainly as oxides, sulphides or carbonates. The ores of many metals are oxides. This is because oxygen is a very reactive element and is very abundant on the earth.

Sapphire is a gemstone, a variety of the mineral corundum, an aluminium oxide. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colours.

Aluminium is the most abundant metal in earth's crust with $\text{percentage by weight = 8.23%}$ followed by iron with $\text{5.63% by weight }$.

The most abundant element in earth's crust is oxygen with$\text{ Percent by weight = 46.1% followed by aluminium with 8.23% by weight.}$
Hence, the answer is option $B$.

Percent abundance of given elements in the earth's crust are :

Iron is the second most abundant metal in the earths crust. It is found in the molten form inside the crust of the earth. In the presence of air and moisture it forms its oxide but the alloy of steel is widely used as pipes,it is unreactive in nature.

Percentage abundance of the given elements in the earth's crust is :