Identify the correct options for the following questions regarding units, significant figures, separation techniques, and chemical properties:

SECTION - A

i) 1 pm = $10^{-12}$ m.
The prefix "pico" (p) denotes $10^{-12}$.
The correct option is b) $10^{-12}$.

ii) The number of significant figures in $1.50 \times 10^4$ g is 3.
In scientific notation, all digits in the coefficient (1.50) are significant. The trailing zero after the decimal point is significant.
The correct option is a) 3.

iii) A mixture of Acetone and Benzene can be separated by fractional distillation.
Acetone and Benzene are miscible liquids with different boiling points (Acetone: 56 °C, Benzene: 80 °C), making fractional distillation an effective separation method.
The correct option is b) Fractional Distillation.

iv) The SI unit of Frequency is Hertz (Hz).
The Hertz is defined as one cycle per second ($s^{-1}$).
The correct option is c) Hz.

v) The type of hybridization in $BF_3$ is $sp^2$.
Boron in $BF_3$ forms three single bonds with fluorine atoms and has no lone pairs. This results in a trigonal planar geometry and $sp^2$ hybridization.
Based on the provided options, assuming 'a)' is intended to be $sp^2$ despite the blurriness, the correct option is a) $sp^2$. (Note: If option 'a)' is strictly $sp^3$, then $sp^2$ is not listed, and the question options are flawed.)

vi) The oxidation number of S in $SO_4^{2-}$ is +6.
Let the oxidation number of S be $x$. The oxidation number of oxygen is typically -2. The overall charge of the ion is -2.

$$x + 4(-2) = -2$$ $$x - 8 = -2$$ $$x = +6$$

The correct option is c) +6.

vii) Which of the following pairs is not isoelectronic?
Isoelectronic species have the same number of electrons.

• a) $Na^+$ (10 electrons) & $Na$ (11 electrons) - Not isoelectronic.
• b) $Mg^{2+}$ (10 electrons) & $Ne$ (10 electrons) - Isoelectronic.
• c) $Al^{3+}$ (10 electrons) & $B^{3+}$ (2 electrons) - Not isoelectronic.
• d) $P^{3-}$ (18 electrons) & $N^{3-}$ (10 electrons) - Not isoelectronic. Since the question asks for a pair that is not isoelectronic, and options a, c, and d all fit this description, the question is ambiguous. However, if only one answer must be chosen, we select the first instance. The correct option is a) $Na^+$ & $Na$.

viii) The composition of syngas is primarily carbon monoxide (CO) and hydrogen ($H_2$).
Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and often some carbon dioxide.
The correct option is a) $CO + 3H_2$.

ix) Borax has formula $Na_2B_4O_7$.
Borax is commonly known as sodium tetraborate decahydrate ($Na_2B_4O_7 \cdot 10H_2O$), but its anhydrous form is $Na_2B_4O_7$. Options b) and d) are identical.
The correct option is **b) $Na_2B_4O_