Question

Arsenic is detected by:
A. ring test
B. Lucas test
C. lake test
D. Marsh test

Answer 1

Arsenic is a metalloid, possessing the properties of both metals and nonmetals. It is denoted by the symbol, $As$ and the atomic number of arsenic is 33. The electronic configuration of arsenic is $\left[ {Ar} \right]3{d^{10}}4{s^2}4{p^3}$. It is placed in the group 15 of the periodic table.

Complete step by step answer:
We have to select the correct test that is used for detecting the presence of arsenic in any sample. Let us first understand the meaning of each test listed above and its uses.
The ring test is the test used for detection of nitrate ions ($N{O_3}^ -$) in any solution. During this test, the solution to be tested is mixed with iron (II) sulphate and then concentrated sulphuric acid (${H_2}S{O_4}$) is slowly added to it, forming a layer below the aqueous solution. The presence of nitrate ions in the solution will be confirmed if a brown ring is formed at the junction of two layers. Hence, this test is also referred to as the brown ring test. Hence, option (A) is incorrect.
The Lucas test is the test used for differentiating between primary, secondary and tertiary alcohols. For this purpose, Lucas reagent is used which contains a solution of anhydrous zinc chloride and concentrated hydrochloric acid. The primary, secondary and tertiary alcohols react with the Lucas reagent at different rates, which is considered as the distinguishing parameter for identifying the type of alcohol. Hence, option (B) is incorrect.
The Lake test is the confirmatory test for detection of $A{l^{3 + }}$ ions. In lake test, water is added to the sample followed by aluminium chloride and aluminium hydroxide. The formation of white precipitate confirms the presence of $A{l^{3 + }}$ ions. Hence, option (C) is incorrect.
The Marsh test is a test used for detecting even a trace amount of arsenic in a given sample. It is a highly sensitive method of detecting arsenic. The method was developed by the chemist James Marsh. The method can be used for detecting the presence of arsenic in food items and stomach contents of humans. During the Marsh test, the sample is treated with sulphuric acid followed by arsenic free zinc in a flask. The mixture is then heated, which forms a mirror beyond the heated area of the flask.
Therefore, arsenic is detected by the Marsh test.

So, the correct answer is Option D.

Additional information:
Arsenic is a well-known poison. It is most poisonous in the form of soluble inorganic compounds. Prolonged intake of the inorganic arsenic compounds may lead to arsenicosis, which is a type of arsenic poisoning.
The seafood is a rich source of organic arsenic compounds. In the organic form, the arsenic compounds are less harmful and can be easily eliminated from the body of the organism.

Note: Whether a person has been exposed to the arsenic recently or not can be confirmed by conducting the urine test of that person. If the same person had consumed seafood recently, the arsenic test for that person may be positive. But, it is not a matter of concern as the arsenic present in seafood in the form of organic compounds. These arsenic containing organic compounds are released by the human body through urine.