Answer:
Here's what I get
Explanation:
1. Nickel sulfate
base + acid ⟶ salt + water
NiSO₄ is a salt of the base Ni(OH)₂ and the acid sulfuric acid.
Hydroxides of transition metals are insoluble; most sulfates are soluble.

2. Carbonate + acid
Most carbonates are insoluble.
They react with acids to form carbonic acid (H₂CO₃), which decomposes into water and carbon dioxide.

Not sure about any others but I believe 3 goes with B
Manganese has 25 electrons and is a transition element
Electronic configuration of the atom describes the arrangemnet of electrons in different shells and subshells ( sublevels).
Now , there are 4 types of sublevels: s, p , d and f . These sublevels have orbital which are spaces with high probability of having an electron and each orbital can have maximum 2 electrons.
Therefore,
s-sublevel has 1 orbital - it can have maximum 2 electrons.
p-sublevel has 3 orbitals - it can have maximum 6 electrons
d-sublevel has 5 orbitals - it can have maximum 10 electrons
f-sublevel has 7 orbitals - it can have maximum 14 electrons.
Hence, the acsending order of sublevels in terms of maximum number of electrons is:
<h2>s < p < d < f</h2>
It uses the voltages and sound freq. in the air to measure the wave lengthths