urgent!!! chemistry questions

1.
The answer is d.

Isomers are different compounds having the same molecular formula.

The molecular formula of pentane is C5H12, the three isomers of pentane are CH3CH2CH2CH2CH3, CH3CH2CH2CH(CH3)2, C(CH3)4. They have the same molecular formula C5H12 (b is incorrect), and thus the same formula mass (a is incorrect). They also have the same empirical formula C5H12 (c is incorrect). However, they have different structural formulae (d is correct).


2.
The answer is c.

Organic compounds are carbon-containing compounds, with few exceptions (such as CO, CO2, H2CO3, CO32-, etc.)


3.
The answer is d.

A more reactive metal can displace a less reactive metal from its salt.

Zn is more reactive than Cr, and thus Zn can displace Cr from Cr3+ salts.
3Zn(s) + 2Cr3+(aq) → 3Zn2+(aq) + 2Cr(s)
In other words, Zn reduces Cr3+ ion to Cr.
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