Four charge $Q _1, Q _2, Q _3$, and $Q _4$, of same magnitude are fixed along the $x$ axis at $x =-2 a - a ,+ a$ and $+2 a$, respectively. A positive charge $q$ is placed on the positive $y$ axis at a distance $b > 0$. Four options of the signs of these charges are given in List-$I$ . The direction of the forces on the charge q is given in List-$II$ Match List-$1$ with List-$II$ and select the correct answer using the code given below the lists.$Image$

List-$I$	List-$II$
$P.$ $\quad Q _1, Q _2, Q _3, Q _4$, all positive	$1.\quad$ $+ x$
$Q.$ $\quad Q_1, Q_2$ positive $Q_3, Q_4$ negative	$2.\quad$ $-x$
$R.$ $\quad Q_1, Q_4$ positive $Q_2, Q_3$ negative	$3.\quad$ $+ y$
$S.$ $\quad Q_1, Q_3$ positive $Q_2, Q_4$ negative	$4.\quad$ $-y$

Two point charges $A$ and $B$, having charges $+Q$ and $- Q$ respectively, are placed at certain distance apart and force acting between them is $\mathrm{F}$. If $25 \%$ charge of $A$ is transferred to $B$, then force between the charges becomes

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Two positive ions, each carrying a charge $q,$ are separated by a distance $d.$ If $F$ is the force of repulsion between the ions, the number of electrons missing from each ion will be  ($e$ being the charge on an electron)

Force between two identical spheres charged with same charge is $F$. If $50\%$ charge of one sphere is transferred to second sphere then new force will be

Write general equation of Coulombian force on ${q_1}$ by system of charges ${q_1},{q_2},.......,{q_n}$.