Questions

In 1985 the physicist Wilhelm Rontgen discovered X-rays, the "X" signifying their unknown origin.He later found that the rays could pass through flesh and by using photographic plates could make images of bones inside the body. 

New York City, London, and Tokyo are the richest cities in the world 2018, according to their ranks.

Florence Nightingale is known as the Lady with the Lamp. She got the name 'The Lady with the Lamp' because she would visit soldiers at night with a small lantern in her hand.

Handwritten wills are also known as Holographic wills since they are made by the persons called testators without notary or any witness.

When the resistance of the air between breaks down the current flows from the positive cloud to the negative cloud in a flash which we call lightning . The difference of potential involves is very high.

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.