The cosine of the angle $A$ of the triangle with vertices $A(1, -1, 2)$, $B(6, 11, 2)$, and $C(1, 2, 6)$ is:

${}^{18}_{8}O$ has a half-life of $4650 \ years$. $200 \ mg$ of a sample of ${}^{18}_{8}O$ is reduced to $25 \ mg$ in .......... $years$.

Given that:
$2C_{(s)} + 2O_{2(g)} \to 2CO_{2(g)}; \Delta H = -787 \ kJ$
$H_{2(g)} + 1/2 O_{2(g)} \to H_2O_{(l)}; \Delta H = -286 \ kJ$
$C_2H_{2(g)} + 2.5 O_{2(g)} \to 2CO_{2(g)} + H_2O_{(l)}; \Delta H = -1301 \ kJ$
Calculate the heat of formation of acetylene $(C_2H_{2(g)})$ in $kJ$.

The conjugate base of $H_2PO_4^-$ is......

$A$ wire elongates by $l \, mm$ when a load $W$ is hanged from it. If the wire goes over a pulley and two weights $W$ each are hung at the two ends,the elongation of the wire will be (in $mm$):

$A$ parallel plate capacitor with plate area $A$ and separation between the plates $d$ is charged by a constant current $I$. Consider a plane surface of area $A/2$ parallel to the plates and drawn between the plates. The displacement current through the area is