The question above is incomplete, the full question is given below:
What additional test would be needed to establish the exact position of hydrogen in the activity series of the following elements: magnesium, zinc, lead, copper and silver.
ANSWER
The position of hydrogen on a reactivity series can be determined by its ability to displace oxygen from the oxide of the metal concerned. If hydrogen is more reactive than a metal, it will displace oxygen from the metal oxide and reduce the metal oxide to its metal. If the metal is more reactive than hydrogen, hydrogen will not be able to reduce the metal oxide to its metal.
Answer:
A disease caused by a plasmodium parasite, transmitted by the bite of infected mosquitoes.
The severity of malaria varies based on the species of plasmodium.
Symptoms are chills, fever, and sweating, usually occurring a few weeks after being bitten.
People traveling to areas where malaria is common typically take protective drugs before, during, and after their trip. Treatment includes antimalarial drugs.
Explanation:

Actually Welcome to the Concept of the Lens and Ray Optics.
We must understand the Concept that,
1.) When a beam of parallel light pass through a Convex lens, all the rays get deviated and converges to a special point at the axis that is a Focus.
2.) When a beam of light passes through the Concave lens,the light beams diverge from one another forming a virtual focus in the primary side of lens,
Hence the above given diagram beam rays are diverging, it is a CONCAVE LENS
answer is C.) Concave lens
The best answer is the first option. A bike rusting is an example of a chemical change since rusting is a chemical reaction. New substances are formed from this reaction. On the other hand, other choices given are just physical changes because only the shape or the physical form of the substances are being changed.