Questions

The size of the pupil of the automatically adjusts itself according to the intensity of light passing through it; if the intensity is more, the size is less, if less, it is more. So in our case the pupil should dilate i.e , increase in size to be able to see in the dark. This switchover takes some time. But here the entry into the dark room is immediate. So the eye has no time to adjust itself and hence is not able to see at all for a while. 

A reflection.

In chemistry, the term transition metal has three possible meanings: The IUPAC definition defines a transition metal as "an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell".

Any of the set of metallic elements occupying a central block (Groups IVB–VIII, IB, and IIB, or 4–12) in the periodic table, e.g. iron, manganese, chromium, and copper. Chemically they show variable valency and a strong tendency to form coordination compounds, and many of their compounds are coloured.

Here in the given options, only iron (Fe) is a transition metal since Strontium is an alkaline earth, arsenic is a metalloid, hydrogen is (normally) a diatomic gas.

A method for providing fault tolerance by using multiple hard disk drives

In a spreadsheet program, when a data is changed all calculations are recalculated.

The nucleotides that are present in DNA molecule are 4. They are Thymine (T), Guanine (G), Adenine (A) and Cytosine (C).

Here in this Adenine pairs with Thymine (A - T) and Cytosine pairs with Guanine (C - G).

The organs protected by the thoracic cage include the lungs and the heart.