The SI unit of electric current is Ampere.
An electric current is said to be one ampere, if one coulomb of electric charge flows through a given area of cross section of a conductor in one second.

The main constituent of biogas is methane. Biogas contains up to 75% of methane.

Element X with atomic number 11 is sodium and its symbol is Na.
Electronic configuration of X is 2, 8, 1.

According to the Dobereiner's law of triads, the atomic mass of the middle element of a triad is the arithmetic mean of the atomic masses of the other two elements.

In human beings, oxygen (O₂₎ and carbon dioxide (CO₂₎ is transported in human beings with the help of a respiratory pigment called haemoglobin. This pigment is present in the red blood cells. During respiration diffusion of oxygen into the blood occurs in the capillaries of the alveoli. The haemoglobin has a high affinity for oxygen. In alveoli, haemoglobin takes up oxygen from the air in the alveoli and transports it to various organs, tissues or cells of the body. In the cell, carbon dioxide moves out of the cell by the process of diffusion and is is transported from the body cell to the lungs in the forms of carboxy-haemoglobin, carbonic acid, bicarbonates of sodium and potassium.

Eye lens is a convex lens. It is a transparent, flexible jelly like material made up of proteins.
The main role of the ciliary muscles is to change the curvature and focal length of the eye lens to focus on near and far objects accordingly.

(i) The formula of oxide of first group elements will be M₂O. Where M represents group 1 element like Li, Na, K etc. The valency of group 1 elements is one as they have one electron in the valence shell whereas valency of oxygen is 2. To complete the octet of oxygen atom, two atoms of group 1 element combine with oxygen; hence the general formula of oxide of group 1 elements is M₂O. Li₂O, Na₂O and K₂O are the some of the oxides of group 1 elements.

(ii) The formula of halides of group 13 elements is MX₃.

Where, M= group 13 elements (B, Al) and X= group 17 elements (Cl, Br, I).

The elements of group 13 have three electrons in the valence shell and their valency is 3. Halogens have 7 valence electrons and their valency is 1. To complete the octet of group 13 elements, three atoms of halogens share 1 electron each, hence the general formula of halide of group 13 elements is MX₃.

(iii) The formula of compound when an element A of group–2 combines with an element B of group–17 is AB₂. The elements of group–2 have 2 electrons in the valence shell and their valency is 2. To complete the octet of group 2 elements, two atoms of group–17 share 1 electron each, hence the general formula of compound is AB₂.