Which of the following reactions are redox reactions?
a. al(s)+3ag+(aq)→al3+(aq)+3ag(s)
b. so3(g)+h2o(l)→h2so4(aq)
c. ba(s)+cl2(g)→bacl2(s)
d. mg(s)+br2(l)→mgbr2(s)

A redox reaction is one in which there is an increase or decrease in oxidation number of species from left to right in the reaction.

A redox reaction is a reaction in which there is a loss and gain of electrons. We must recall that a redox reaction is a synchronous process. The loss and gain of electrons occurs at the same time.

In a redox reaction, the oxidation numbers of species are increased or decreased accordingly. In the reactions;

the oxidation number of species increased from left to right or  decreased from left to right therefore they are redox reactions.

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Options A, C and D.

Explanation:

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. It is represented by an increase in the oxidation number.

Reduction is the loss of electrons during a reaction by a molecule, atom or ion. It is represented by a decrease in the oxidation number.

Both processes makes up what we know as Redox (REDuction - OXidation) reactions.

Note: The oxidation number of an element in its ground state is 0.

To identify which reactions are redox, we look out for change in oxidation number of the molecule, atom or ions involved.

A) Al has an increase in oxidation number for 0 (reactant side) to +3 (product side), Silver moves from +1(reactant) to 0 (product side). this means Al was oxidized and Ag+ was reduced. This is a redox reaction.

B) All atoms involved retains their oxidation number. S= +6, O =-2, H =+1. This is not a redox reaction.

C) Ba has an increase in oxidation number form 0 to +2, while Cl has a decrease in oxidation number form 0 to -2. This is a redox reaction.

D) Mg has an increase in oxidation number form 0 to +2, while Br has a decrease in oxidation number form 0 to -2. This is a redox reaction.

there is none because earth is stationary and flat.

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.