Explanation:
A period 3 element is one of the chemical elements in the third row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when the periodic table skips a row and a chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon. The first two, sodium and magnesium, are members of the s-block of the periodic table, while the others are members of the p-block. All of the period 3 elements occur in nature and have at least one stable isotope.[1]
The dense aerosol cloud created caused decreases in the amount of solar radiation that reached the Earths surface.
Answer:
c. Cr
Explanation:

The compound is containing
ion.
If acid reacts with it, CO_2 evolves.

therefore, Cr would form a precipitate when added to an aqueous solution of this compound. Cr2CO3 is the precipitate.
Since the volume decreased, it means that the pressure is going to rise. Thus, the equilibrium of the reaction will shift in the direction that has the least amount of moles.
Explanation:
2,4-DNP is negative: aldehyde and ketone absent
Chromic acid is negative: alcohol absent.
KMnO4 test negative: alkene absent
The only positive result is for Fe(OH)2.
Nitro group-containing compounds react with ferrous hydroxide to give amine and ferric hydroxide red ppt. Hence given compound contains the nitro group (-NO2).